Improved contention mechanism for access to random resource units in an 802.11 channel

ABSTRACT

In an 802.11ax network with an access point, a trigger frame offers random resource units to nodes for data uplink communication to the access point. To dynamically adapt the contention mechanism used by the nodes to access the random resource units, the AP updates a correcting TBD parameter at each new TXOP and includes the updated adjusting parameter in the trigger frame for the next TXOP. The nodes use the TBD parameter to generate a local random RU backoff value from a contention window range, for contending for access to the random resource units. The TBD parameter may directly impact the contention window size CWO or boundaries values of a selection range from which CWO is selected.

FIELD OF THE INVENTION

The present invention relates generally to communication networks andmore specifically to the contention-based access of channels and theirsplitting sub-channels (or Resource Units) that are available to a groupof nodes.

The invention finds application in wireless communication networks, inparticular to the access of an 802.11ax composite channel and of OFDMAResource Units forming for instance an 802.11ax composite channel forUplink communication. One application of the method regards wirelessdata communication over a wireless communication network using CarrierSense Multiple Access with Collision Avoidance (CSMA/CA), the networkbeing accessible by a plurality of node devices.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC standard defines the way Wireless local areanetworks (WLANs) must work at the physical and medium access control(MAC) level. Typically, the 802.11 MAC (Medium Access Control) operatingmode implements the well-known Distributed Coordination Function (DCF)which relies on a contention-based mechanism based on the so-called“Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA)technique.

The 802.11 medium access protocol standard or operating mode is mainlydirected to the management of communication nodes waiting for thewireless medium to become idle so as to try to access to the wirelessmedium.

The network operating mode defined by the IEEE 802.11ac standardprovides very high throughput (VHT) by, among other means, moving fromthe 2.4 GHz band which is deemed to be highly susceptible tointerference to the 5 GHz band, thereby allowing for wider frequencycontiguous channels of 80 MHz to be used, two of which may optionally becombined to get a 160 MHz channel as operating band of the wirelessnetwork.

The 802.11ac standard also tweaks control frames such as theRequest-To-Send (RTS) and Clear-To-Send (CTS) frames to allow forcomposite channels of varying and predefined bandwidths of 20, 40 or 80MHz, the composite channels being made of one or more channels that arecontiguous within the operating band. The 160 MHz composite channel ispossible by the combination of two 80 MHz composite channels within the160 MHz operating band. The control frames specify the channel width(bandwidth) for the targeted composite channel.

A composite channel therefore consists of a primary channel on which agiven node performs EDCA backoff procedure to access the medium, and ofat least one secondary channel, of for example 20 MHz each.

EDCA defines traffic categories and four corresponding access categoriesthat make it possible to handle differently high-priority trafficcompared to low-priority traffic.

Implementation of EDCA in the nodes can be made using a plurality oftraffic queues for serving data traffic at different priorities, withwhich a respective plurality of queue backoff engines is associated. Thequeue backoff engines are configured to compute respective queue backoffvalues when the associated traffic queue stores data to transmit.

Thanks to the EDCA backoff procedure, the node can thus access thecommunication network using contention type access mechanism based onthe computed queue backoff values.

The primary channel is used by the communication nodes to sense whetheror not the channel is idle, and the primary channel can be extendedusing the secondary channel or channels to form a composite channel.

Sensing of channel idleness is made using CCA (clear channelassessment), and more particularly CCA-ED, standing for CCA-EnergyDetect. CCA-ED is the ability of any node to detect non-802.11 energy ina channel and back off data transmission. An ED threshold based in whichthe energy detected on the channel is compared is for instance definedto be 20 dB above the minimum sensitivity of the PHY layer of the node.If the in-band signal energy crosses this threshold, CCA is held busyuntil the medium energy becomes below the threshold anew.

Given a tree breakdown of the operating band into elementary 20 MHzchannels, some secondary channels are named tertiary or quaternarychannels.

In 802.11ac, all the transmissions, and thus the possible compositechannels, include the primary channel. This is because the nodes performfull Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) andNetwork Allocation Vector (NAV) tracking on the primary channel only.The other channels are assigned as secondary channels, on which thenodes have only capability of CCA (clear channel assessment), i.e.detection of an idle or busy state/status of said secondary channel.

An issue with the use of composite channels as defined in the 802.11n or802.11ac (or 802.11ax) is that the 802.11n and 802.11ac-compliant nodes(i.e. HT nodes standing for High Throughput nodes) and the other legacynodes (i.e. non-HT nodes compliant only with for instance 802.11a/b/g)have to co-exist within the same wireless network and thus have to sharethe 20 MHz channels.

To cope with this issue, the 802.11n and 802.11ac standards provide thepossibility to duplicate control frames (e.g. RTS/CTS or CTS-to-Self orACK frames to acknowledge correct or erroneous reception of the sentdata) on each 20 MHz channel in an 802.11a legacy format (called as“non-HT”) to establish a protection of the requested TXOP over the wholecomposite channel.

This is for any legacy 802.11a node that uses any of the 20 MHz channelinvolved in the composite channel to be aware of on-going communicationson the 20 MHz channel. As a result, the legacy node is prevented frominitiating a new transmission until the end of the current compositechannel TXOP granted to an 802.11n/ac node.

As originally proposed by 802.11n, a duplication of conventional 802.11aor “non-HT” transmission is provided to allow the two identical 20 MHznon-HT control frames to be sent simultaneously on both the primary andsecondary channels forming the used composite channel.

This approach has been widened for 802.11ac to allow duplication overthe channels forming an 80 MHz or 160 MHz composite channel. In theremainder of the present document, the “duplicated non-HT frame” or“duplicated non-HT control frame” or “duplicated control frame” meansthat the node device duplicates the conventional or “non-HT”transmission of a given control frame over secondary 20 MHz channel(s)of the (40 MHz 80 MHz or 160 MHz) operating band.

In practice, to request a composite channel (equal to or greater than 40MHz) for a new TXOP, an 802.11n/ac node does an EDCA backoff procedurein the primary 20 MHz channel as mentioned above. In parallel, itperforms a channel sensing mechanism, such as a Clear-Channel-Assessment(CCA) signal detection, on the secondary channels to detect thesecondary channel or channels that are idle (channel state/status is“idle”) during a PIFS interval before the start of the new TXOP (i.e.before any queue backoff counter expires).

More recently, Institute of Electrical and Electronics Engineers (IEEE)officially approved the 802.11ax task group, as the successor of802.11ac. The primary goal of the 802.11ax task group consists inseeking for an improvement in data speed to wireless communicatingdevices used in dense deployment scenarios.

Recent developments in the 802.11ax standard sought to optimize usage ofthe composite channel by multiple nodes in a wireless network having anaccess point (AP). Indeed, typical contents have important amount ofdata, for instance related to high-definition audio-visual real-time andinteractive content. Furthermore, it is well-known that the performanceof the CSMA/CA protocol used in the IEEE 802.11 standard deterioratesrapidly as the number of nodes and the amount of traffic increase, i.e.in dense WLAN scenarios.

In this context, multi-user transmission has been considered to allowmultiple simultaneous transmissions to/from different users in bothdownlink and uplink directions. In the uplink to the AP, multi-usertransmissions can be used to mitigate the collision probability byallowing multiple nodes to simultaneously transmit.

To actually perform such multi-user transmission, it has been proposedto split a granted channel into sub-channels, also referred to asresource units (RUs), that are shared in the frequency domain bymultiple users, based for instance on Orthogonal Frequency DivisionMultiple Access (OFDMA) technique. Each RU may be defined by a number oftones, the 80 MHz channel containing up to 996 usable tones.

OFDMA is a multi-user variation of OFDM which has emerged as a new keytechnology to improve efficiency in advanced infrastructure-basedwireless networks. It combines OFDM on the physical layer with FrequencyDivision Multiple Access (FDMA) on the MAC layer, allowing differentsubcarriers to be assigned to different nodes in order to increaseconcurrency. Adjacent sub-carriers often experience similar channelconditions and are thus grouped to sub-channels: an OFDMA sub-channel orRU is thus a set of sub-carriers.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

As currently envisaged, the granularity of such OFDMA sub-channels isfiner than the original 20 MHz channel band. Typically, a 2 MHz or 5 MHzsub-channel may be contemplated as a minimal width, therefore definingfor instance 9 sub-channels or resource units within a single 20 MHzchannel.

To support multi-user uplink, i.e. uplink transmission to the 802.11axaccess point (AP) during the granted TxOP, the 802.11ax AP has toprovide signaling information for the legacy nodes (non-802.11ax nodes)to set their NAV and for the 802.11ax nodes to determine the allocationof the resource units RUs.

It has been proposed for the AP to send a trigger frame (TF) to the802.11ax nodes to trigger uplink communications.

The document IEEE 802.11-15/0365 proposes that a ‘Trigger’ frame (TF) issent by the AP to solicit the transmission of uplink (UL) Multi-User(OFDMA) PPDU from multiple nodes. In response, the nodes transmit UL MU(OFDMA) PPDU as immediate responses to the Trigger frame. Alltransmitters can send data at the same time, but using disjoint sets ofRUs (i.e. of frequencies in the OFDMA scheme), resulting intransmissions with less interference.

The bandwidth or width of the targeted composite channel is signaled inthe TF frame, meaning that the 20, 40, 80 or 160 MHz value is added. TheTF frame is sent over the primary 20 MHz channel and duplicated(replicated) on each other 20 MHz channels forming the targetedcomposite channel, if appropriate. As described above for theduplication of control frames, it is expected that every nearby legacynode (non-HT or 802.11ac nodes) receiving the TF on its primary channel,then sets its NAV to the value specified in the TF frame. This preventsthese legacy nodes from accessing the channels of the targeted compositechannel during the TXOP.

A resource unit RU can be reserved for a specific node, in which casethe AP indicates, in the TF, the node to which the RU is reserved. SuchRU is called Scheduled RU. The indicated node does not need to performcontention on accessing a scheduled RU reserved to it.

In order to better improve the efficiency of the system in regards toun-managed traffic to the AP (for example, uplink management frames fromassociated nodes, unassociated nodes intending to reach an AP, or simplyunmanaged data traffic), the document IEEE 802.11-15/0604 proposes a newtrigger frame (TF-R) above the previous UL MU procedure, allowing randomaccess onto the OFDMA TXOP. In other words, the resource unit RU can berandomly accessed by more than one node (of the group of nodesregistered with the AP). Such RU is called Random RU and is indicated assuch in the TF. Random RUs may serve as a basis for contention betweennodes willing to access the communication medium for sending data.

An exemplary random resource selection procedure is defined in documentIEEE 802.11-15/1105. According to this procedure, each 802.11ax nodemaintains a dedicated backoff engine, referred below to as OFDMA or RU(for resource unit) backoff engine, to contend for access to the randomRUs. The dedicated OFDMA or RU backoff, also called OBO, is randomlyassigned in a contention window range [0, CWO] wherein CWO is thecontention window size defined in a range [CWO_(min), CWO_(max)].

Once the OFDMA or RU backoff value reaches zero in a node (it isdecremented at each new TF-R frame by the number of random RUs definedtherein for instance), the node becomes eligible for RU access and thusrandomly selects one RU from among all the random RUs defined in thereceived trigger frame. It then uses the selected RU to transmit data ofat least one of the traffic queues.

The management of the OFDMA or RU backoff engine is not optimal.

SUMMARY OF INVENTION

As the nodes access the RUs on a random basis, the risk that eithernodes collide on the same RU, or some RUs are not used, or both is high.

For instance, there is no guarantee that the Scheduled and Random RUswill be used by the nodes.

It is particularly the case for the Random RUs because any rule used bythe nodes to select a Random RU may result in having RUs not allocatedat all to any node. Also, the AP does not know whether or not some nodesneed bandwidth. In addition, some RUs provided by the AP may not beaccessible for some nodes because of hidden legacy nodes.

It is also the case for the Scheduled RUs (which are reserved by the APbecause some nodes have explicitly requested bandwidth) if the specifiednodes do not send data.

It results that the channel bandwidth is not optimally used.

On the other hand, depending on the contention procedure used by thenodes to randomly access the Random RUs, it may happen that nodes selectthe same RUs and thus collide.

To reduce the risk, a desired access rule may be deployed over the nodesto drive the random access as desired. For instance, the same mappingmay be implemented in each node to map a local random value, such as theconventional local backoff counter or the OBO value, onto the RU havingthe same index value in the composite channel (for instance based on anordering index of the RUs within the composite channel), which mapped RUis thus selected for access by the node.

However, the use of an access rule may not be satisfactory toefficiently reduce the risk, in particular because the network evolvesover time: the number of nodes registered in the AP evolves over time,the number of nodes having data to upload to the AP, etc. Due to suchnetwork evolution, an access rule relevant at a first time may prove notto be relevant at a later time.

The inventors have also observed that the OFDMA or RU backoff scheme forrandom RU contention is not optimal given its coexistence with the EDCAqueue backoff schemes for CSMA/CA contention.

For instance, it is undisputable that the OFDMA or RU backoff schemeruns in parallel to the EDCA queue backoff schemes. It means that somedata (e.g. dedicated to the AP) in an EDCA traffic queue may betransmitted through any of the two access procedures: EDCA providing anew TxOP, and UL OFDMA providing a new random (or scheduled) RU. Ofcourse, uplink traffics are not the only ones in a basic service set(BSS) made of the AP and its registered nodes; there may existpeer-to-peer or direct traffics in between registered nodes of the BSS.

This is why the inventors believe that the interaction between the OFDMAor RU backoff scheme and the EDCA queue backoff schemes should beexploited in a better way to manage efficient use of the random OFDMARUs.

In addition, while QoS (Quality of Service) is provided by EDCA thanksto the traffic differentiation, this is believed that UL OFDMA mediumaccess misses QoS.

It is a broad objective of the improvements according to the presentinvention to provide improved communication methods and devices in acommunication network, such as a wireless network. The communicationnetwork includes a plurality of nodes, possibly including an AccessPoint with which the other nodes have registered, all of them sharingthe physical medium of the communication network.

The present improvements has been devised to overcome one or moreforegoing limitations, in particular to provide communication methodshaving improved use of random and/or scheduled RUs. This may result inhaving more efficient usage of the network bandwidth (of the RUs) withlimited risks of collisions.

The improvements can be applied to any communication network, e.g. awireless network, in which random resource units are available throughcontention-based access, within a granted transmission opportunity. Forinstance, an access point to which a transmission opportunity has beengranted provides the registered nodes with a plurality of sub-channels(or resource units) forming the granted communication channel. Thecommunication channel is the elementary channel on which the nodesperform sensing to determine whether it is idle or busy.

The improvements according to the invention is especially suitable fordata uplink transmission from nodes to the AP of an IEEE 802.11axnetwork (and future version), in which case the random RUs may beaccessed using OFDMA. Embodiments of the invention may also applybetween nodes (without AP), as well as in any communication networkother than 802.11ax provided that it offers random RUs or the like thatcan be accessed simultaneously (and thus through a contention approach)by the nodes.

Multiple technics can be used to determine and to manage the dedicatedOFDMA backoff value OBO. Most often the OBO backoff is driven throughits associated contention window size CWO. In that case, the inventorshave contemplated using two modes to drive the value CWO defining thecontention window size: first, a fully local mode that drives thecomputation of CWO by each node locally; and second, an AP-initiatedmode that drives the computation of CWO by the access point (AP), inparticular by sending a correcting or TBD parameter to drive the nodesin defining their own contention window size.

However, the inventors have noticed that the most efficient mode is notalways the same, depending on network conditions, for instance thenumber of available random RUs or the number of nodes competing foraccessing the random RUs. FIG. 8 illustrates simulation curves of theevolution of an RU use efficiency metric depending on the number of thecompeting nodes. One may note that in some network configurations, thefully local mode is more efficient than the AP-initiated mode, and thatin other network configurations, the balance of efficiency is reversed.

In this context, there is a need to provide more efficient usage of thenetwork bandwidth (of the RUs) with limited risks of collisions whilehandling correctly such various modes. In other words, there is an issueof selecting the most appropriate mode to drive the computation of CWOat the nodes, in order to optimize the use of the random RUs.

Main embodiments of first improvements according to the inventionprovide, from the access point's perspective, a wireless communicationmethod in a wireless network comprising an access point and a pluralityof nodes, the method comprising the following steps, at the accesspoint:

sending one or more trigger frames to the nodes, each trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, each trigger frame defining resourceunits forming the communication channel and including a plurality ofrandom resource units that the nodes access using a contention schemebased on a contention window to transmit data;

determining use statistics on the use of the random resource units bythe nodes during the one or more transmission opportunities;

determining, based on the determined use statistics, a TBD parameter todrive nodes in defining (i.e. determining) their own contention windowsize;

evaluating a measure of use efficiency of the random resource unitsbased on the determined use statistics; and

deciding, based on the evaluated use efficiency measure, to transmit ornot, to the nodes, the determined TBD parameter within a next triggerframe for reserving a next transmission opportunity.

The next trigger frame (TF) embedding the TBD parameter is notnecessarily adjacent to one previous TF having a TBD parameter. Forinstance, a conventional TF may be sent there between. Also conventionalRTS/CTS exchanges may occur between two trigger frames according to thefirst main embodiments (i.e. including the TBD parameter).

The same main embodiments of the invention provide, from the node'sperspective, a wireless communication method in a wireless networkcomprising an access point and a plurality of nodes, the methodcomprising the following steps, at one of said nodes:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, the trigger frame defining resourceunits forming the communication channel and including a plurality ofrandom resource units that the nodes access using a contention schemebased on a contention window to transmit data;

determining whether or not the received trigger frame includes a TBDparameter to drive the node in defining its own contention window size;

in case of positive determining, computing a new contention window sizebased on the received TBD parameter; otherwise, using a local contentionwindow size as new contention window size, to contend for access to therandom resource units splitting the transmission opportunity; and

transmitting data to the access point upon accessing one of the randomresource units.

The access point evaluates a use efficiency metric to determine whetherit is opportune to drive the computation of the contention window sizeby the access point (first mode), or it is more opportune to let thenodes handling such computation by their own (second mode).

In the first mode, the AP's overall view of the whole wireless networkmakes it possible to obtain more efficient contention windows range atthe nodes, in order to reduce risks of collisions and thus to improveuse of the random RUs.

In the second mode, the nodes handle the computation of their contentionwindow sizes by their own. This makes it possible to take advantage oflocal specificities that help using efficiently the random RUs. It isfor instance the case with hidden nodes. In particular, an AP whichcannot see legacy nodes in the vicinity of some nodes contending foraccess to the random RUs, is not able to take into account such hiddenlegacy nodes to adjust the contention window size at the nodes. As aconsequence, it may be worth having the nodes computing independentlytheir own CWO by themselves.

As a consequence, the decision to switch from one mode to the other,given the efficiency of RU use due to the current mode, helps to improvesuch use of the random RUs as the network conditions evolve over time.

Correlatively, the invention provides a communication device acting asan access point in a wireless network also comprising a plurality ofnodes, the communication device acting as an access point comprising atleast one microprocessor configured for carrying out the steps of:

sending one or more trigger frames to the nodes, each trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, each trigger frame defining resourceunits forming the communication channel and including a plurality ofrandom resource units that the nodes access using a contention schemebased on a contention window to transmit data;

determining use statistics on the use of the random resource units bythe nodes during the one or more transmission opportunities;

determining, based on the determined use statistics, a TBD parameter todrive nodes in defining their own contention window size;

evaluating a measure of use efficiency of the random resource unitsbased on the determined use statistics; and

deciding, based on the evaluated use efficiency measure to transmit ornot, to the nodes, the determined TBD parameter within a next triggerframe for reserving a next transmission opportunity.

From the node's perspective, the invention also provides a communicationdevice in a wireless network comprising an access point and a pluralityof nodes, the communication device being one of the nodes and comprisingat least one microprocessor configured for carrying out the steps of:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, the trigger frame defining resourceunits forming the communication channel and including a plurality ofrandom resource units that the nodes access using a contention schemebased on a contention window to transmit data;

determining whether or not the received trigger frame includes a TBDparameter to drive the node in defining its own contention window size;

in case of positive determining, computing a new contention window sizebased on the received TBD parameter; otherwise, using a local contentionwindow size as new contention window size, to contend for access to therandom resource units splitting the transmission opportunity; and

transmitting data to the access point upon accessing one of the randomresource units.

Optional features of embodiments of the first improvements are explainedhere below with reference to a method, while they can be transposed intosystem features dedicated to any node device according to embodiments ofthe first improvements.

In embodiments, the access point switches from a current mode among afirst mode (AP-initiated) in which the determined TBD parameter istransmitted within a trigger frame and a second mode (local) in whichthe determined TBD parameter is not transmitted, to the other mode whenthe evaluated use efficiency measure falls below a first predefinedefficiency threshold.

In particular, the current mode may be locked until an evaluated useefficiency measure reaches a second predefined efficiency threshold.

In specific embodiments, in the second mode, the transmitted nexttrigger frame includes a TBD parameter field set to undefined, forinstance using a specific value. This is a way to define absence of aTBD parameter that is easily detectable by the nodes.

In other embodiments from the access point's perspective, the evaluateduse efficiency measure is function of a number of random resource unitsthat are used by the nodes and that do not experience collision duringthe one or more transmission opportunities.

In specific embodiments, the evaluated use efficiency measure includes aratio between said number of random resource units that are used by thenodes and that do not experience collisions, and a total number ofrandom resource units available during the one or more transmissionopportunities.

In other words, the decision to switch between the two modes definedabove is based on statistics related to the random resource units thatare efficiently used to transmit data, i.e. data that are positivelyacknowledged by the access point. As a consequence, a relevant metric onnetwork efficiency is used.

In variants, the evaluated use efficiency measure is function of anumber of unused random RUs and/or of a number of collided random RUs inthe one or more transmission opportunities. For instance, the evaluateduse efficiency measure may include a ratio between a number of collidedrandom resource units and the total number of random resource unitsavailable during the one or more transmission opportunities. Or, theevaluated use efficiency measure may include a ratio between a number ofunused random resource units and the total number of random resourceunits available during the one or more transmission opportunities.

In embodiments from the nodes' perspective, the method may furthercomprises computing, based on the new contention window size, an RUbackoff value to be used to contend for access to the random resourceunits in order to transmit data.

In specific embodiments, computing the RU backoff value includesrandomly selecting a value within a contention window range defined bythe new contention window size, and the new contention window size isdetermined based on the TBD parameter received from the access point incase of positive determining. Thus, the AP drives the computation of thecontention window size or range, and consequently drives the way thenodes contend for access to the random RUs.

In embodiments, the TBD parameter is an RU collision and unuse factorreflecting the access point's point of view regarding the usage ofrandom resource units defined in one or more previous trigger frames.

In specific embodiments, the TBD parameter is based on a number ofunused random RUs and/or of a number of collided random RUs in the oneor more transmission opportunities.

In variants, the TBD parameter is function of a number of randomresource units that are used by the nodes and that do not experiencecollision during the one or more transmission opportunities. It is forinstance the same ratio as defined above for the use efficiency measure.

Various embodiments rely on computing CWO as follows in case of positivedetermining (i.e. based on the TBD parameter): CWO=2^(CRF)*CWO_(min),wherein CRF=α*(Nb_collided_RU/Nb_RU_total) and CWO_(min) is a(predetermined) low boundary value. For instance, CWO_(min) is (or moregenerally may be determined as a function of) the number of randomresource units defined in the next trigger frame. It means that the newcontention window size (at the node) is determined as a function of thenumber of random resource units defined in the received trigger frame.

Thus in some embodiments from the AP's perspective, the TBD parameter isfunction of a ratio between the number of collided random RUs(Nb_collided_RU above) and the number of random RUs in the one or moretransmission opportunities (Nb_RU_total above). In particular, the ratiomay be multiplied by a predefined factor α, for instance the predefinedfactor equals 0.08.

The TBD parameter may thus equal the ratio multiplied by the predefinedfactor, i.e. equal to CRF. From the node's perspective, it means thatthe new contention window size is equal to 2^(TBD)*CWO_(min), whereinTBD is the TBD parameter received from the access point.

In a variant, the TBD parameter equals 2̂CRF (i.e. 2^(CRF)). From thenode's perspective, it means that the new contention window size isequal to TBD*CWO_(min), where TBD is the TBD parameter received from theaccess point.

In another variant, the TBD parameter directly defines CWO, i.e. a newcontention window size to be used by the nodes. From the node'sperspective, it means that the new contention window size CWO is the TBDparameter received from the access point.

In variants that do not necessarily rely on the above formulaCWO=2^(CRF)*CWO_(min), the TBD parameter identifies an entry to selectin a predefined table of contention window sizes. The table may beshared between the AP and the nodes. Thus, from the node's perspective,the new contention window size is selected as an entry of a predefinedtable of contention window sizes, wherein the TBD parameter receivedfrom the access point identifies the entry to select in the predefinedtable.

In yet other variants, the range from which CWO is selected may bedefined using the TBD parameter. Indeed, CWO is selected from[CWO_(min), CWO_(max)].

For instance, the TBD parameter defines a lower boundary CWO_(min) of aselection range from which the nodes select their contention windowsizes to use to contend for access to the random resource units. Fromthe node's perspective, the new contention window size is selected froma selection range, and the lower boundary of the selection range is theTBD parameter received from the access point.

According to embodiments, the TBD parameter defines an upper boundaryCWO_(max) of a selection range from which the nodes select theircontention window sizes to use to contend for access to the randomresource units. From the node's perspective, the new contention windowsize is selected from a selection range, and the upper boundary of theselection range is the TBD parameter received from the access point.

In other embodiments from the access point's perspective, the determinedTBD parameter is assigned to a group of nodes. The assignment may bemade by specifying a BSSID, Basic Service Set Identification, in thenext trigger frame including the determined TBD parameter. Indeed, an APcan handle different BSSIDs corresponding to different virtualsub-networks of nodes. Thus, the above provision helps the AP to controlthe QoS and priorities of some groups of nodes.

From the node's perspective, it means that the determining step includeschecking whether a TBD parameter included in the received trigger frameis assigned to a group of nodes to which the node belongs. Inparticular, the checking step may include reading a BSSID, Basic ServiceSet Identification, in the received trigger frame.

In other embodiments, the TBD parameter is assigned to a type of data tobe transmitted by the nodes. The AP can thus manage the latency of agiven type of transmitted data.

In some embodiments from the node's perspective, the local contentionwindow size is updated depending on a success or failure in transmittingthe data.

In embodiments, the local contention window size is set to a(predetermined) low boundary value in case of transmission success. Thisis to offer the best access to the random RUs as long as there is nodifficulty (failure) when transmitting data.

In particular, the low boundary value is the number of random resourceunits defined in the received trigger frame.

In some of the second embodiments, the local contention window size isdoubled in case of transmission failure.

In specific embodiments, the local contention window size is determinedas a function of the number CWO_(min) of random resource units definedin a received trigger frame.

The doubling-based embodiments above correspond to the local contentionwindow size equaling CWO_(min)*2^(n), where n is the number ofsuccessive transmission failures by the node.

In other embodiments, the local contention window size equalsCWO_(min)(t)*2^(n), where n is the number of successive transmissionfailures by the node and CWO_(min)(t) is the number of random resourceunits defined in a current trigger frame received at time t.

First main embodiments of second improvements of the invention provide,from the access point's perspective, a wireless communication method ina wireless network comprising an access point and a plurality of nodes,the method comprising the following steps, at the access point:

sending one or more trigger frames to the nodes, each trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, each trigger frame defining resourceunits forming the communication channel and including a plurality ofrandom resource units that the nodes access using a contention scheme;

determining statistics (i.e. at least one item of information) on randomresource units not used by the nodes during the one or more transmissionopportunities and/or on random resource units on which nodes collideduring the one or more transmission opportunities;

determining a TBD parameter based on the determined statistics,

sending, to the nodes, a next trigger frame for reserving a nexttransmission opportunity, the next trigger frame including thedetermined TBD parameter.

The next trigger frame (TF) embedded the TBD parameter is notnecessarily adjacent to one previous TF having a TBD parameter. Forinstance, a conventional TF may be sent there between. Also conventionalRTS/CTS exchanges may occur between two trigger frames according to thefirst main embodiments (i.e. including the TBD parameter).

The same first main embodiments of the second improvements provide, fromthe node's perspective, a wireless communication method in a wirelessnetwork comprising an access point and a plurality of nodes, the methodcomprising the following steps, at one of said nodes:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network and including a TBD parameter, thetrigger frame defining resource units forming the communication channeland including a plurality of random resource units that the nodes accessusing a contention scheme;

determining, based on the TBD parameter and on one random parameterlocal to the node, one of the random resource units (this stepcorresponds to the way the nodes contend for access to the randomresource units according to the first embodiments of the invention);

transmitting data to the access point using the determined randomresource unit.

In these first main embodiments, a correcting or TBD parameter isexchanged between the access point and the nodes. On one hand, it isused by the nodes to adjust how the local random parameter impacts thechoice of the random RUs to be used. This is why the parameter is named“correcting”. On the other hand, this TBD parameter is calculated by theaccess point based on statistics related to the use of the Random RUs(unused or collided RUs). This is because the access point has anoverall view of the network, as the nodes only communicate with it.

It results that the contention scheme used by the nodes to access theRandom RUs can be dynamically adapted to the network environment. As aconsequence, more efficient usage of the network bandwidth (of the RUs)with limited risks of collisions can be achieved.

Correlatively, the invention provides a communication device acting asan access point in a wireless network also comprising a plurality ofnodes, the communication device acting as an access point comprising atleast one microprocessor configured for carrying out the steps of:

sending one or more trigger frames to the nodes, each trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, each trigger frame defining resourceunits forming the communication channel and including a plurality ofrandom resource units that the nodes access using a contention scheme;

determining statistics on random resource units not used by the nodesduring the one or more transmission opportunities and/or random resourceunits on which nodes collide during the one or more transmissionopportunities;

determining a TBD parameter based on the determined statistics,

sending, to the nodes, a next trigger frame for reserving a nexttransmission opportunity, the next trigger frame including thedetermined TBD parameter.

From the node's perspective, the second improvements also provide acommunication device in a wireless network comprising an access pointand a plurality of nodes, the communication device being one of thenodes and comprising at least one microprocessor configured for carryingout the steps of:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network and including a TBD parameter, thetrigger frame defining resource units forming the communication channeland including a plurality of random resource units that the nodes accessusing a contention scheme;

determining, based on the TBD parameter and on one random parameterlocal to the node, one of the random resource units;

transmitting data to the access point using the determined randomresource unit.

Optional features of embodiments of the second improvements are definedin the appended claims. Some of these features are explained here belowwith reference to a method, while they can be transposed into systemfeatures dedicated to any node device according to embodiments of thesecond improvements.

In embodiments, the TBD parameter is function of a number of unusedrandom resource units and/or of a number of collided random resourceunits. These embodiments make it possible to dynamically adapt tovarious deficient network environments.

In variant, the TBD parameter is function of a number of random resourceunits that are used by the nodes and that do not experience collisionduring the one or more transmission opportunities. In fact, this numberis directly linked to the above numbers of unused and collided randomRUs, because the sum of all of them equals the number of random RUs.

In embodiments, the TBD parameter is function of the number of nodeshaving data to transmit during the next transmission opportunity. Insome situations, such number of nodes having data to transmit may beapproximate to the number of nodes transmitting in the one or more(previous) transmission opportunities.

Such number of nodes having data to transmit directly impacts the riskof collisions and/or of unused RUs, in particular if the number of RUsforming the composite channel is known in advance.

In embodiments, the method at the access point further comprisesmodifying the number of random resource units within the communicationchannel for the next transmission opportunity, based on the determinedstatistics (this is equivalent to being based on the transmitted TBDparameter). The AP may thus adjust the number of Random RUs as thenetwork conditions evolve.

In embodiments from the access point's perspective, the TBD parameterincludes a value to apply to a random parameter local to each node, forthe node to determine which one of the random resource units to access.For instance, the random parameter may be based on a backoff value usedby the node to contend for access to the communication channel. Thisbackoff value is for instance the conventional 802.11 backoff counterused to contend for network access to the 20 MHz channels or the RUbackoff value defined above.

These embodiments keep compliance with the 802.11 standard, as thebackoff counter is still used. In addition, they provide an efficientrandom mechanism for contention that can be dynamically adjusted in avery simple way.

In variants, the TBD parameter includes a number of random resourceunits not used during the one or more transmission opportunities or aratio of this number to the total number of random resource units in theone or more transmission opportunities.

In other variants, the TBD parameter includes a number of randomresource units on which nodes collide during the one or moretransmission opportunities or a ratio of this number to the total numberof random resource units in the one or more transmission opportunities.The two variants may be combined.

In yet another variant, the TBD parameter includes a number of randomresource units that are used by the nodes and that do not experiencecollision during the one or more transmission opportunities or a ratioof this number to the total number of random resource units in the oneor more transmission opportunities.

In embodiments from the node's perspective, the random parameter localto the node is based on a backoff value used by the node to contend foraccess to the communication channel (i.e. a value corresponding to thenumber of time-slots the node waits before accessing the communicationmedium).

In embodiments from the node's perspective, the random resource unitshave respective unique indexes (for instance an ordering index), anddetermining one of the random resource units includes applying the TBDparameter to the local random parameter, the result of which identifyingthe index of the random resource unit to be used to transmit the data tothe access point. Note that, as described above, the local randomparameter can be the backoff counter used by the node to contend foraccess to the communication channel.

These embodiments provide a simple way to perform random contention onthe RUs, while keeping compliance with 802.11 standard.

In a specific embodiment, applying the TBD parameter to the local randomparameter includes dividing the local random parameter by the TBDparameter and outputting an integer rounding of the division result.This is to provide a simple mechanism to dynamically adjust thecontention scheme to the network conditions (through the use of thestatistics and TBD parameter at the access point).

According to embodiments at the access point, the sent TBD parameterdefines a parameter for defining a contention window size CWO in thenodes.

From the node's perspective, where the node includes an RU backoffengine for computing an RU backoff value to be used to contend foraccess to at least one random resource unit splitting the transmissionopportunity reserved on the communication channel, in order to transmitdata stored in a traffic queue, this corresponds for the node to performthe following step:

computing the RU backoff value by randomly selecting a value within acontention window range defined by a contention window size, wherein thecontention window size is determined based on the TBD parameter receivedfrom the access point.

Again, this approach dynamically adjusts the node contention to therandom RUs, to an overall view of the network conditions as analyzed bythe access point.

In the context of EDCA queue backoff schemes, the node includes:

a plurality of traffic queues for serving data traffic at differentpriorities; and

a plurality of queue backoff engines, each associated with a respectivetraffic queue for computing a respective queue backoff value to be usedto contend for access to the communication network in order to transmitdata stored in the respective traffic queue;

and the RU backoff engine is separate from the queue backoff engines.

In embodiments from the node's perspective, the TBD parameter receivedfrom the access point is an RU collision and unuse factor reflecting theaccess point's point of view regarding the usage of random resourceunits defined in one or more previous trigger frames.

In specific embodiments from the node's perspective, the TBD parameteris based on a number of unused random RUs and/or of a number of collidedrandom RUs in the one or more previous trigger frames. In other wordsfrom the AP, the sent TBD parameter is based (i.e. is determined based)on a number of unused random RUs and/or of a number of collided randomRUs in the one or more transmission opportunities.

In variants, the TBD parameter is function of a number of randomresource units that are used by the nodes and that do not experiencecollision during the one or more transmission opportunities.

Various sub-embodiments rely on computing CWO as follows:CWO=2^(CRF*CWO) _(min), wherein CRF=α*(Nb_collided_RU/Nb_RU_total) andCWO_(min) is a (predetermined) low boundary value. For instance,CWO_(min) is (or more generally may be determined as a function of) thenumber of random resource units defined in the next trigger frame. Itmeans that the contention window size (at the node) is determined as afunction of the number of random resource units defined in the receivedtrigger frame.

Thus in some embodiments from the AP's perspective, the sent TBDparameter is function of a ratio between the number of collided randomRUs (Nb_collided_RU above) and the number of random RUs in the one ormore transmission opportunities (Nb_RU_total above). In particular, theratio may be multiplied by a predefined factor α, for instance thepredefined factor equals 0.08.

The sent TBD parameter may thus equal the ratio multiplied by thepredefined factor, i.e. equal to CRF. From the node's perspective, itmeans that the contention window size is equal to 2^(TBD)*CWO_(min),wherein TBD is the TBD parameter received from the access point.

In a variant, the sent TBD parameter equals 2̂CRF (i.e. 2^(CRF)). Fromthe node's perspective, it means that the contention window size isequal to TBD*CWO_(min), where TBD is the TBD parameter received from theaccess point.

In another variant, the sent TBD parameter directly defines CWO, i.e. acontention window size to be used by the nodes. From the node'sperspective, it means that the contention window size CWO is the TBDparameter received from the access point.

In variants that do not necessarily rely on the above formulaCWO=2^(CRF)*CWO_(min), the sent TBD parameter identifies an entry toselect in a predefined table of contention window sizes. The table maybe shared between the AP and the nodes. Thus, from the node'sperspective, the contention window size is selected as an entry of apredefined table of contention window sizes, wherein the TBD parameterreceived from the access point identifies the entry to select in thepredefined table.

In yet other variants, the selection range from which CWO is selectedmay be defined using the TBD parameter. Indeed CWO is selected from[CWO_(min), CWO_(max)].

For instance, the sent TBD parameter defines a lower boundary CWO_(min)of a selection range from which the nodes select their contention windowsizes to use to contend for access to the random resource units. Fromthe node's perspective, the contention window size is selected from aselection range, and the lower boundary of the selection range is theTBD parameter received from the access point.

According to embodiments, the sent TBD parameter defines an upperboundary CWO_(max) of a selection range from which the nodes selecttheir contention window sizes to use to contend for access to the randomresource units. From the node's perspective, the contention window sizeis selected from a selection range, and the upper boundary of theselection range is the TBD parameter received from the access point.

According to embodiments, the TBD parameter is assigned to a group ofnodes, for instance to a BSSID handled by the AP. This is for the AP tocontrol the QoS and priorities of some groups of nodes.

According to embodiments, the TBD parameter is assigned to a type ofdata to be transmitted by the nodes. The AP can thus manage the latencyof a given type of transmitted data.

In embodiments still from the node's perspective, the method may furthercomprise the steps of:

determining a first time instant based on the random parameter local tothe node; and

sending padding data on the determined random resource unit from thedetermined first time instant up to the end of a predetermined timewindow after having received the trigger frame,

start transmitting the data on the determined random resource unit whenthe predetermined time window ends.

These embodiments offer an efficient contention mechanism while keepingsynchronization between the nodes. Indeed, all the nodes starttransmitting their data to the access point from the same time instant(when the time window ends). Such synchronization is particularlyimportant in case of OFDMA RUs.

Various declinations of these embodiments are defined and explainedbelow with reference to the second main embodiments of the secondimprovements.

Second main embodiments of the second improvements of the inventionprovide a wireless communication method in a wireless network comprisingan access point and a plurality of nodes, the method comprising thefollowing steps, at one of said nodes:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, the trigger frame defining resourceunits forming the communication channel including a plurality of randomresource units that the nodes access using a contention scheme;

determining a first time instant based on one random parameter local tothe node;

sending padding (or dummy) data on a first one of the random resourceunits from the determined first time instant up to the end of apredetermined time window after having received the trigger frame (thedetermining and sending steps thus forming a mechanism for contendingfor access to the RUs according to embodiments of the invention);

starting transmitting data to the access point on the first randomresource unit when the predetermined time window ends (it defines apredefined second time instant).

The second embodiments define a new contention mechanism for access toRUs composing a conventional communication channel, for instance a 20MHz 802.11 channel. They are mainly implemented at the nodes.

They particularly apply to OFDMA RUs. This is because, due tosynchronization requirements between the OFDMA symbols (or PPDUs), thenodes implementing the second embodiments of the invention only sendpadding data. The padding data are sent up to a time point (predefinedsecond time instant) at which all the nodes having data to transmitsimultaneously start transmitting the data. Synchronization is thussaved, while having an efficient contention scheme to access the RandomRUs.

Note that the nodes being allocated with a respective Scheduled RU inthe communication channel should also wait for the end of the timewindow before transmitting their data. “Wait” may also mean sendingpadding data on the Scheduled RU.

Correlatively, the invention provides a communication device in awireless network comprising an access point and a plurality of nodes,the communication device being one of the nodes and comprising at leastone microprocessor configured for carrying out the steps of:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, the trigger frame defining resourceunits forming the communication channel including a plurality of randomresource units that the nodes access using a contention scheme;

determining a first time instant based on one random parameter local tothe node;

sending padding (or dummy) data on a first one of the random resourceunits from the determined first time instant up to the end of apredetermined time window after having received the trigger frame (thedetermining and sending steps thus forming a mechanism for contendingfor access to the RUs according to embodiments of the invention);

starting transmitting data to the access point on the first randomresource unit when the predetermined time window ends (it defines apredefined second time instant).

Optional features of embodiments of the second improvements are definedin the appended claims. Some of these features are explained here belowwith reference to a method, while they can be transposed into systemfeatures dedicated to any node device according to embodiments of thesecond improvements.

In embodiments, the local random parameter is based on a backoff valueused by the node to contend for access to the communication channel(i.e. a value corresponding to the number of time-slots the node waitsbefore accessing the communication medium, for instance a 20 MHzchannel). This is a simple way to obtain a local random parameter, whilekeeping compliancy with the 802.11 standard.

In specific embodiments, the first time instant is determined as alinear function of the backoff value (local random parameter) within thetime window. As an example, the method may further comprise decrementingthe backoff value (local random parameter) each elementary time unitwithin the time window, and the first time instant is the time instantat which the backoff value (local random parameter) reaches zero. Inother words, the nodes may perform contention on the Random RUs usingtheir conventional 802.11 backoff counter. Note that the elementary timeunits used to decrement the backoff value during contention to accessthe RUs may be different in size (in particular shorter) compared to thetime units used when contending for access to the (20 MHz) communicationchannel. This is to shorten the required time window and thus toincrease the actual transmission duration dedicated to useful data.

In specific embodiments, if the backoff value (local random parameter)does not reach zero at the end of the time window, no random resourceunit is selected for sending padding data and transmitting data withinthe transmission opportunity.

In embodiments, the time window is calculated based on a number ofelementary time units corresponding to the number of random resourceunits in the communication channel. For instance, the same number ofelementary time units as the number of random resource units may beused. This is to avoid that too many nodes try to access a limitednumber of Random RUs.

In a particular embodiment, the time window is further calculated basedon an adjusting parameter, which adjusting parameter is function ofstatistics on random resource units not used by the nodes during one ormore previous transmission opportunities and/or random resource units onwhich nodes collide during one or more previous transmissionopportunities. In other words, the time window size is adjustedaccording to the network conditions (statistics). The statistics may bedefined and used as described above with reference to the firstembodiments of the invention.

In embodiments, the method may further comprise sensing a use of therandom resource units during the time window (in particular until thefirst time instant). Use of a random RU means that an OFDM symbol isdetected by the node on the RU. Note that the implementation of thesecond embodiments of the invention results in having OFDM symbols madeof padding data.

In a particular embodiment, the method further comprises selecting oneof the random resource units sensed as unused to send the padding dataand transmit the data. This is to efficiently use the network bandwidthwith limited collisions.

According to a specific implementation, the random resource units areordered within the communication channel (they have respective uniqueindexes), and the selected unused random resource unit is the first oneof the sensed unused random resource units according to the order. Withthis approach, only one random resource unit is newly used each time thelocal random parameter is evaluated anew. A control may thus be achievedto propose a new unused random resource unit at each new evaluation ofthe local random parameter within the time window.

In another particular embodiment (which may be combined), the methodfurther comprise, upon sensing a new random resource unit as used,updating the local random parameter. This provision makes it possible tospeed up the RU allocation for the remaining time (for instance if theupdate consists in decreasing the local random parameter).

According to a specific implementation, the local random parameter isupdated based on at least one TBD parameter specified in the triggerframe received from the access point. Such TBD parameter may be asdefined above with reference to the first main embodiments. Thisconfiguration helps optimizing the use of the Random RUs, since such TBDparameter may be set by the access point based on statisticsrepresentative of the network environment.

For instance, the TBD parameter is function of statistics on randomresource units not used by the nodes during one or more previoustransmission opportunities and/or random resource units on which nodescollide during one or more previous transmission opportunities.

In a yet other particular embodiment (which also may be combined), assoon as all the random resource units of the at least one communicationchannel are sensed as used, stopping the sensing step (also thedecrementing step when implemented). This is to avoid useless processingas soon as no further Random RUs is available.

In embodiments, a backoff value used by the node to contend for accessto the communication channel is updated based on the value taken by thelocal random parameter at the determined first time instant. The backoffvalue may be the conventional 802.11 backoff counter used to contend foraccess to the 20 MHz channels.

This provision optimizes use of the network. This is because, since thelocal random parameter has evolved while been evaluated over the timewindow, some nodes have already sent their data. It results that theyare less chances that nodes succeed in contending for access to thecommunication channel in the first next backoff time slots. To avoidwasting such first backoff time slots, the backoff counter of the nodesmay thus be updated according to the evolution of their local randomparameter.

As noted above, no first time instant may be obtained for some nodes,for instance if the contention mechanism does not give an access tothose nodes during the time window. For such nodes, a backoff value usedby the node to contend for access to the communication channel is alsoupdated based on the value taken by the local random parameter at theend of the time window in case no first time instant has beendetermined.

In embodiments, the duration of the time window is specified in thetrigger frame received from the access point. It makes it possible forthe access point to efficiently drive the contention mechanism at thenodes.

In embodiments, the received trigger frame includes a TBD parameter, andthe method further comprises determining the first random resource unitbased on the TBD parameter and on the local random parameter. Asdescribed above for the first main embodiments of the secondimprovements, this configuration helps adapting dynamically thecontention scheme used by the nodes to access the Random RUs, to thenetwork environment. As a consequence, more efficient usage of thenetwork bandwidth (of the RUs) with limited risks of collisions can beachieved.

Of course, all the embodiments described above with reference to thefirst main embodiments for the second improvements may apply to thisconfiguration.

Third improvements of the invention provide a wireless communicationmethod in a wireless network comprising an access point and a pluralityof nodes, the method comprising the following steps, at one of saidnodes:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, the trigger frame defining resourceunits forming the communication channel including a plurality of randomresource units that the nodes access using a contention scheme, whereinthe node includes an RU backoff engine for computing an RU backoff valueto be used to contend for access to the random resource units, in orderto transmit data,

based on a current RU backoff value, accessing a random resource unit totransmit data to the access point,

after having transmitted the data, computing a new RU backoff value tocontend for new access to random resource units, the RU backoff valuebeing a value randomly selected within a contention window range definedby a contention window size, wherein the contention window size isupdated depending on a success or failure in transmitting the data.

Thanks to this updating of the contention window size CWO, transmissionsin case of collisions are gradually limited, which in turn reduces theprobability of collisions and thus improves use of the communicationnetwork.

Correlatively, the third improvements provide a communication device ina wireless network comprising an access point and a plurality of nodes,the communication device being one of the nodes and comprising at leastone microprocessor configured for carrying out the steps of:

receiving a trigger frame from the access point, the trigger framereserving a transmission opportunity on at least one communicationchannel of the wireless network, the trigger frame defining resourceunits forming the communication channel including a plurality of randomresource units that the nodes access using a contention scheme, whereinthe node includes an RU backoff engine for computing an RU backoff valueto be used to contend for access to the random resource units, in orderto transmit data,

based on a current RU backoff value, accessing a random resource unit totransmit data to the access point,

after having transmitted the data, computing a new RU backoff value tocontend for new access to random resource units, the RU backoff valuebeing a value randomly selected within a contention window range definedby a contention window size, wherein the contention window size isupdated depending on a success or failure in transmitting the data.

Optional features of embodiments of the third improvements are explainedhere below with reference to a method, while they can be transposed intosystem features dedicated to any node device according to embodiments ofthe third improvements.

In embodiments, the contention window size is set to a (predetermined)low boundary value in case of transmission success. This is to offer thebest access to the random RUs as long as there is no difficulty(failure) when transmitting data.

In particular, the low boundary value is the number of random resourceunits defined in a received trigger frame, for instance in the lastreceived trigger frame.

In some of the second embodiments, the contention window size is doubledin case of transmission failure.

In specific embodiments, the contention window size is determined as afunction of the number CWO_(min) of random resource units defined in areceived trigger frame.

The doubling-based embodiments above correspond to the contention windowsize equaling CWO_(min)*2^(n), where n is the number of successivetransmission failures.

In other embodiments, the contention window size equalsCWO_(min)(t)*2^(n), where n is the number of successive transmissionfailures and CWO_(min)(t) is the number of random resource units definedin a current trigger frame received at time t.

In yet other embodiments, the contention window size is determined as afunction of an RU collision factor built locally. The RU collisionfactor may reflect the local node's point of view regarding how therandom RUs are used, i.e. reflect statistics on collisions on the randomRUs it uses.

In specific embodiments, the method further comprises updating the localRU collision factor depending on a success or failure in transmittingthe data, for instance by setting it to a minimum value or dividing itby two in case of transmission success and doubling it in case oftransmission failure. This is to build a local factor that efficientlyreflects the local node's point of view regarding the use of the randomRUs.

In specific embodiments, the method further comprises computing a newvalue for the contention window size and a new RU backoff value uponreceiving a new trigger frame following the step of transmitting data.In these embodiments, the values are computed only when a newtransmission opportunity comes (through a new trigger frame). This is tostick on the current states or conditions of the nodes and the network.Indeed, the network conditions and EDCA queue filing may substantiallyevolve from one time to the other.

In some embodiments, computing the RU backoff value includes randomlyselecting a value within a contention window range [0, CWO], wherein CWOis the contention window size for the RU backoff value.

Fourth improvements of the invention also seek to improved use of randomRUs, in particular in a context of a plurality of traffic queues, suchas EDCA queues. The fourth improvements of the invention provide acommunication method in a communication network comprising a pluralityof nodes, at least one node comprising:

a plurality of traffic queues for serving data traffic at differentpriorities;

a plurality of queue backoff engines, each associated with a respectivetraffic queue for computing a respective queue backoff value to be usedto contend for access to at least one communication channel in order totransmit data stored in the respective traffic queue. Such queue backoffvalue may be computed either when an empty traffic queue starts storingnew data to transmit, or when a transmission of data of a traffic queueends if there are still data to transmit in the traffic queue; and

an RU backoff engine separate from the queue backoff engines, forcomputing an RU backoff value to be used to contend for access to atleast one random resource unit splitting a transmission opportunitygranted on the communication channel, in order to transmit data storedin either traffic queue,

the method comprising; at said node:

determining one or more RU backoff parameters based on one or more queuebackoff parameters of the queue backoff engines; and

computing the RU backoff value from the determined one or more RUbackoff parameters.

Correspondingly, embodiments of the invention provide a communicationdevice forming node in a communication network, comprising:

a plurality of traffic queues for serving data traffic at differentpriorities;

a plurality of queue backoff engines, each associated with a respectivetraffic queue for computing a respective queue backoff value to be usedto contend for access to at least one communication channel in order totransmit data stored in the respective traffic queue;

an RU backoff engine separate from the queue backoff engines andconfigured to compute an RU backoff value to be used to contend foraccess to at least one random resource unit splitting a transmissionopportunity granted on the communication channel, in order to transmitdata stored in either traffic queue,

wherein the RU backoff engine is further configured to:

determine one or more RU backoff parameters based on one or more queuebackoff parameters of the queue backoff engines; and

compute the RU backoff value from the determined one or more RU backoffparameters.

Note that the node may actually access the communication network usingcontention type access mechanism based on the computed queue backoffvalues (EDCA-based CMSA/CA access) and access the one or more randomresources units defined in a trigger frame, using contention type accessmechanism based on the RU backoff value (OFDMA access) or scheduledaccess, the accesses being in order to transmit data of at least one ofthe traffic queues.

By using the queue backoff parameters, the RU backoff value that appliedto all traffic queues may thus include some traffic prioritization,thereby improving efficiency of usage of random RUs and QoS of the OFDMAaccess.

It results that the node can manage a randomized prioritization forlocal traffic (EDCA compliancy) along with a proper backoff for OFDMAmedium access, without requiring new prioritization parameters to be setfor OFDMA medium access. In addition, the approach according to thefourth improvements may keep compliancy with 802.11ax and be implementedwithin conventional environments (i.e. without change in the EDCA statemachine).

Optional features of embodiments of the fourth improvements areexplained here below with reference to a method, while they can betransposed into system features dedicated to any node device accordingto embodiments of the fourth improvements.

In some embodiments involving the determination of RU backoff parametersas defined above:

-   -   the one or more queue backoff parameters used to determine the        one or more RU backoff parameters are parameters of queue        backoff engines associated with a traffic queue storing data to        transmit. In other words, only the parameters of active EDCA        traffics are taken into account. The contention-based RU access        thus advantageously reflects the traffic prioritization of the        data that are currently available for transmission; and/or    -   the one or more RU backoff parameters include a size of a        contention window range from which the RU backoff value is        computed. This is usually the value CWO defining the contention        window range [0, CWO] from which the backoff value is randomly        selected. As a consequence, initialization of the RU backoff        parameters for random RU contention depends on the EDCA        traffics.

In specific embodiments, the contention window size for the RU backoffvalue is selected within an interval [CWO_(min), CWO_(max)], wherein atleast one of CWO_(min) and CWO_(max) is an RU backoff parameterdetermined based on one or more queue backoff parameters. As thecontention window size CWO is determined within an interval thatdirectly depends on the queue backoff parameters, it also dependsindirectly on the same queue backoff parameters.

According to a particular feature, both CWO_(min) and CWO_(max) are RUbackoff parameters determined based on one or more queue backoffparameters. This makes it possible to strictly bind the contentionwindow size depending on the current EDCA parameters for CSMA/CAcontention.

According to another particular feature, CWO_(max) is one from:

an upper boundary of a selection range (This is the range from which acontention window size is selected. It is a queue backoff parameter) ofthe queue backoff engine having the lowest non-zero queue backoff value(i.e. whose traffic queue stores data to transmit). That is the queuebackoff engine associated with the highest priority active traffic(Access Category), in the meaning that it is the first AC to transmit onthe network. The node advantageously takes the same highest priority forits contention-based RU access scheme;

a mean of upper boundaries of selection ranges of the queue backoffengines having non-zero queue backoff values (i.e. active AccessCategories or traffic queues having data to transmit). The nodeadvantageously takes a medium priority, and is thus more relaxedcompared to the first proposed value, and

the highest upper boundaries from selection ranges of the queue backoffengines having non-zero queue backoff values. The node is even morerelaxed. In addition, this proposed value avoids the contention-based RUaccess to have a medium priority lower than EDCA-based CSMA/CAcontention scheme.

According to yet another particular feature, CWO_(min) is one or acombination of:

the number of random resource units defined in a received trigger frameand,

the lowest lower boundaries from selection ranges of the queue backoffengines having non-zero queue backoff values.

According to yet another particular feature, a formula used to determineat least one of CWO_(min) and CWO_(max) from one or more queue backoffparameters depends on an RU collision and unuse factor received fromanother node (preferably from an Access Point). The RU collision andunuse factor may reflect the other nodes' point of view regarding howthe random RUs are used, in particular with respect to the number ofunused random RUs and of the number of collided random RUs, in theprevious one or more trigger frames (history of trigger frames).

This approach using the RU collision and unuse factor makes it possibleto dynamically adapt the RU backoff parameters (from which the RUbackoff value for RU contention is determined) to the networkconditions.

In some embodiments, the method further comprises:

transmitting data of at least one of the traffic queues upon accessingone random resource unit based on the RU backoff value (conventionallythe RU backoff value is decremented from time to time);

updating the contention window size depending on a success or failure intransmitting the data (which can be determined based on anacknowledgment message); and

computing a new RU backoff value based on the updated contention windowsize.

In this approach, the RU backoff parameters for the UL-OFDMA randombackoff procedure are continuously adjusted. As a parameter for theadjustments includes success/failure of the UL-OFDMA transmissions asperceived by the addressee node (usually the AP), this approach may thusreduce the probability of RU collision.

In specific embodiments, the contention window size is set to a(predetermined) low boundary value in case of transmission success. Thislow value may for instance be the CWO_(min) value defined above. Thisapproach thus favors transmissions in case no collision is detected.This improves use of the communication network.

In a variant to setting directly the CW size to the (predetermined) lowvalue, it may be decided to divide the current CW size by two (whilekeeping an integer value equal or above the predetermined low value).

In other specific embodiments, the contention window size is doubled,for instance CWO=2×(CWO+1)−1 where CWO is the contention window size, incase of transmission failure. Again, this approach restrictstransmissions in case of collisions, which in turn reduces theprobability of collisions and thus improves use of the communicationnetwork.

In some embodiments, the contention window size is determined as afunction of the number of random resource units defined in a receivedtrigger frame.

In other embodiments, the contention window size is determined as afunction of an RU collision and unuse factor either received fromanother node (preferably from an Access Point) or built locally in caseno factor is received from another node. Again, the RU collision andunuse factor may reflect the other node or the local node's point ofview regarding how the random RUs are used.

In specific embodiments, the method further comprises:

transmitting data of at least one of the traffic queues upon accessingone random resource unit based on the RU backoff value;

updating the local RU collision and unuse factor depending on a successor failure in transmitting the data, for instance by setting it to aminimum value or dividing it by two in case of transmission success anddoubling it in case of transmission failure. This is to build a localfactor that efficiently reflects the local node's point of viewregarding the use of the random RUs. Again, the RU collision and unusefactor may reflect the other node or the local node's point of viewregarding how the random RUs are used.

In specific embodiments, the method further comprises computing a newvalue for the contention window size and a new RU backoff value uponreceiving a new trigger frame following the step of transmitting data.In these embodiments, the values are computed only when a newtransmission opportunity comes (through a new trigger frame). This is tostick on the current states or conditions of the nodes and the network.Indeed, the network conditions and EDCA queue filing may substantiallyevolve from one time to the other.

In specific embodiments, the contention window size is equal to

2^(TBD)×CWO_(min), wherein TBD is the RU collision and unuse factor andCWO_(min) is a (predetermined) low boundary value. This formula providesgood results, in particular because it makes it possible to use theoptimum value CWO_(min) while enabling to slightly correct or adapt itaccording to TBD parameter reflecting network conditions.

In some embodiments, computing the RU backoff value includes randomlyselecting a value within a contention window range [0, CWO], wherein CWOis the contention window size for the RU backoff value.

In specific embodiments, computing the RU backoff value further includesapplying an RU collision and unuse factor received from another node(preferably from an Access Point) to the randomly selected value. Again,the RU collision and unuse factor may reflect the other node's point ofview regarding how the random RUs are used. More efficient usage of thecommunication network may thus be obtained.

In other specific embodiments, computing the RU backoff value furtherincludes adding, to the randomly selected value, a value computed fromone or more arbitration interframe spaces, AIFS, associated withrespective queue backoff engines. This is to take into account therelative priority of some different queue buffers, in particular theactive ones.

In some embodiments, the method further comprises, upon receiving atrigger frame, decrementing the RU backoff value based on the number ofrandom resource units defined in the received trigger frame. Thus, arandom resource unit can be accessed as soon as the RU backoff valuereaches zero or becomes less than zero.

In specific embodiments, decrementing the RU backoff value is also basedon an RU collision and unuse factor received from another node(preferably from an Access Point). Again, the RU collision and unusefactor may reflect the other node's point of view regarding how therandom RUs are used.

In some embodiments, new RU backoff parameters and a new RU backoffvalue to be used to contend for access to at least one random resourceunits in order to transmit data stored in either traffic queue aredetermined upon detecting a triggering event, the triggering event beingone from:

receiving a new trigger frame defining a number of random resource unitsthat is different from a current known number of random resource units(e.g. from the number of RUs defined in a previous trigger frame);

detecting that an empty traffic queue from the plurality of trafficqueues has now received data to transmit;

receiving a positive or negative acknowledgment of a previoustransmission of data in an RU;

receiving a new trigger frame; and

detecting a change in at least one queue backoff parameter used todetermine the one or more RU backoff parameters.

This provision dynamically adapts the contention-based RU access on thenetwork and node evolutions.

In some embodiments, the RU collision and unuse factor is function ofthe number of unused random resource units and of the number of collidedrandom resource units in one or more previous trigger frames. In otherwords, it represents statistics on random resource units not used by thenodes during one or more previous transmission opportunities and/orrandom resource units on which nodes collide during one or more previoustransmission opportunities.

In other embodiments, the random resource units are accessed using OFDMAwithin the communication channel. It means that the random RUs areprovided by splitting the communication channel on a frequency basis.

In yet other embodiments, the communication network is an 802.11axnetwork.

In some embodiments, the method further comprises receiving a triggerframe from an access point in the communication network, the triggerframe reserving the transmission opportunity on the communicationchannel (on behalf of another node, usually the access point) anddefining resource units, RUs, forming the communication channelincluding the at least one random resource unit.

In another approach of the fourth improvements, it is sought to improvethe OFDMA or RU backoff scheme with respects to the network conditions.

In this context, the other approach of the fourth improvements providesa communication method in a communication network comprising an accesspoint and a plurality of nodes, at least one node comprising:

a plurality of traffic queues for serving data traffic at differentpriorities;

a plurality of queue backoff engines, each associated with a respectivetraffic queue for computing a respective queue backoff value to be usedto contend for access to the communication network in order to transmitdata stored in the respective traffic queue. Such queue backoff valuemay be computed either an empty traffic queue starts storing new data totransmit or when a transmission of data of a traffic queue ends if datato transmit remain in the traffic queue; and

an RU backoff engine separate from the queue backoff engines, forcomputing an RU backoff value to be used to contend for access to atleast one random resource unit splitting a transmission opportunitygranted on the communication channel, in order to transmit data storedin either traffic queue,

the method comprising, at the node: computing the RU backoff value byrandomly selecting a value within a contention window range,

wherein at least a size of the contention window range is determinedbased on at least one indication received from the access point.

As a consequence, the contention window range and thus the RU backoffvalue used to contend for RU access may be adapted to the networkconditions as analyzed by the AP.

Correspondingly, the other approach of the fourth improvements providesa communication device forming node in a communication networkcomprising an access point and a plurality of nodes, comprising:

a plurality of traffic queues for serving data traffic at differentpriorities;

a plurality of queue backoff engines, each associated with a respectivetraffic queue for computing a respective queue backoff value to be usedto contend for access to the communication network in order to transmitdata stored in the respective traffic queue;

an RU backoff engine separate from the queue backoff engines, forcomputing an RU backoff value to be used to contend for access to atleast one random resource unit splitting a transmission opportunitygranted on the communication channel, in order to transmit data storedin either traffic queue, computing the RU backoff value includingrandomly selecting a value within a contention window range,

wherein at least a size of the contention window range is determinedbased on at least one indication received from the access point.

Of course, this other approach of the fourth improvements may becombined with the previous approach of the fourth improvements definedabove (and their variations).

Optional features are explained here below with reference to a method,while they can be transposed into system features dedicated to any nodedevice according to the other approach of the fourth improvements.

In embodiments, the indication received from the access point is an RUcollision and unuse factor reflecting the access point's point of viewregarding the usage of random resource units defined in one or moreprevious trigger frames.

In specific embodiments, the collision and unuse factor is based on anumber of unused random RUs and/or of a number of collided random RUs inthe one or more previous trigger frames.

In other embodiments, the size of the contention window range isdetermined based on the indication received from the access point.Indeed, usually a [0, CWO] contention window range is used, meaning thatonly the size CWO can be determined.

In yet other embodiments, the method further comprises receiving atrigger frame from the access point in the communication network, thetrigger frame reserving the transmission opportunity on thecommunication channel and defining resource units, RUs, forming thecommunication channel including the at least one random resource unit.According to a specific feature, the size of the contention window rangeis determined as a function of the number of random resource unitsdefined in the received trigger frame.

In specific embodiments, the size of the contention window range isequal to 2^(TBD)×CWO_(min), wherein TBD is the RU collision and unusefactor received from the access point and CWO_(min) is a (predetermined)low boundary value.

In any improvement according to the invention, the random and/orscheduled resource units are accessed using OFDMA within thecommunication channel. This complies with 802.11ax multi-user uplinkcommunication.

Another aspect of the invention relates to a wireless communicationsystem having an access point and at least one communication deviceforming node as defined above.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device of a communicationnetwork, causes the device to perform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the methods and node devices.

Another aspect of the invention relates to a communication method in acommunication network comprising a plurality of nodes, substantially asherein described with reference to, and as shown in, FIG. 8a , or FIG.8b , or FIGS. 8a and 9, or FIGS. 8b and 10, or FIGS. 8a and 11, or FIGS.8b and 11, or FIGS. 8a, 8b and 11, or FIGS. 8a, 8b , 9, 10 and 11, orFIG. 18, or FIG. 19, or FIG. 20, or FIG. 21, or FIGS. 14, 15, 16 and 18,or FIGS. 14, 15, 16 and 19, or FIGS. 9, 10, 11 and 21 of theaccompanying drawings.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a typical wireless communication system in whichembodiments of the invention may be implemented;

FIG. 2 is a timeline schematically illustrating a conventionalcommunication mechanism according to the IEEE 802.11 standard;

FIGS. 3a, 3b and 3c illustrate the IEEE 802.11e EDCA involving accesscategories;

FIG. 4 illustrates 802.11ac channel allocation that support channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

FIG. 5 illustrates an example of 802.11ax uplink OFDMA transmissionscheme, wherein the AP issues a Trigger Frame for reserving atransmission opportunity of OFDMA sub-channels (resource units) on an 80MHz channel as known in the art;

FIG. 6 shows a schematic representation a communication device orstation in accordance with embodiments of the present invention;

FIG. 7 shows a schematic representation of a wireless communicationdevice in accordance with embodiments of the present invention;

FIG. 8a illustrates, using a flowchart, general steps of a wirelesscommunication method at one of the nodes (not the AP) according to afirst exemplary embodiment of the invention;

FIG. 8b illustrates, using a flowchart, general steps of a wirelesscommunication method at one of the nodes (not the AP) according to asecond exemplary embodiment of the invention;

FIG. 9 illustrates exemplary communication lines according to the firstexemplary embodiment of FIG. 8 a;

FIG. 10 illustrates exemplary communication lines according to thesecond exemplary embodiment of FIG. 8 b;

FIG. 11 illustrates, using a flowchart, general steps of a wirelesscommunication method at the AP adapted to the first and/or secondexemplary embodiments;

FIG. 12 illustrates an exemplary format for an information Elementdedicated to the transmission of parameter values from the AP to thenodes in embodiments of the invention;

FIG. 13 illustrates an exemplary transmission block of a communicationnode according to embodiments of the invention;

FIG. 14 illustrates, using a flowchart, main steps performed by a MAClayer of a node, when receiving new data to transmit, in firstembodiments of the invention;

FIG. 15 illustrates, using a flowchart, main steps for setting an RUbackoff parameter, namely contention window size CWO for OFDMAcontention, in first embodiments of the invention;

FIG. 13 illustrates, using a flowchart, steps of accessing the mediumbased on the conventional EDCA medium access scheme, in firstembodiments of the invention;

FIG. 17 illustrates, using a flowchart, exemplary steps for updating RUbackoff parameters and value upon receiving a positive or negativeacknowledgment of a multi-user OFDMA transmission, in first embodimentsof the invention;

FIG. 18 illustrates, using a flowchart, first exemplary embodiments ofaccessing the medium based on the OFDMA medium access scheme, and oflocally updating the RU backoff parameters, such as the contentionwindow size CWO, when a new trigger frame is received;

FIG. 19 illustrates, using a flowchart, second exemplary embodiments ofaccessing the medium based on the OFDMA medium access scheme, and ofupdating the RU backoff parameters, either locally or based on areceived TBD parameter, when a new trigger frame is received;

FIG. 20 illustrates, using a flowchart, steps of a wirelesscommunication method at the access point;

FIG. 20a illustrates a variant of the process of FIG. 20;

FIG. 21 illustrates, using a flowchart, third exemplary embodiments ofaccessing the medium based on the OFDMA medium access scheme, and ofupdating the RU backoff parameters, either locally or based on areceived TBD parameter, when a new trigger frame is received; and

FIG. 22 illustrates, using curves obtained by simulation, the evolutionof a random-RU efficiency metric depending on the number of the nodescontending for accessing the random RUs.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

FIG. 1 illustrates a communication system in which several communicationnodes (or stations) 101-107 exchange data frames over a radiotransmission channel 100 of a wireless local area network (WLAN), underthe management of a central station, or access point (AP) 110. The radiotransmission channel 100 is defined by an operating frequency bandconstituted by a single channel or a plurality of channels forming acomposite channel.

Access to the shared radio medium to send data frames is based on theCSMA/CA technique, for sensing the carrier and avoiding collision byseparating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtualmechanisms. Virtual carrier sensing is achieved by transmitting controlframes to reserve the medium prior to transmission of data frames.

Next, a source or transmitting node first attempts through the physicalmechanism, to sense a medium that has been idle for at least one DIFS(standing for DCF InterFrame Spacing) time period, before transmittingdata frames.

However, if it is sensed that the shared radio medium is busy during theDIFS period, the source node continues to wait until the radio mediumbecomes idle.

To access the medium, the node starts a countdown backoff counterdesigned to expire after a number of timeslots, chosen randomly in thecontention window range [0, CW], CW (integer) being also referred to asthe Contention Window size and defining the upper boundary of thebackoff selection interval (contention window range). This backoffmechanism or procedure is the basis of the collision avoidance mechanismthat defers the transmission time for a random interval, thus reducingthe probability of collisions on the shared channel. After the backofftime period, the source node may send data or control frames if themedium is idle.

One problem of wireless data communications is that it is not possiblefor the source node to listen while sending, thus preventing the sourcenode from detecting data corruption due to channel fading orinterference or collision phenomena. A source node remains unaware ofthe corruption of the data frames sent and continues to transmit theframes unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positiveacknowledgement (ACK) of the sent data frames by the receiving node ifthe frames are received with success, to notify the source node that nocorruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame,immediately after a period of time called Short InterFrame Space (SIFS).

If the source node does not receive the ACK within a specified ACKtimeout or detects the transmission of a different frame on the channel,it may infer data frame loss. In that case, it generally reschedules theframe transmission according to the above-mentioned backoff procedure.

To improve the Collision Avoidance efficiency of CSMA/CA, a four-wayhandshaking mechanism is optionally implemented. One implementation isknown as the RTS/CTS exchange, defined in the 802.11 standard.

The RTS/CTS exchange consists in exchanging control frames to reservethe radio medium prior to transmitting data frames during a transmissionopportunity called TXOP in the 802.11 standard as described below, thusprotecting data transmissions from any further collisions.

FIG. 2 illustrates the behaviour of three groups of nodes during aconventional communication over a 20 MHz channel of the 802.11 medium:transmitting or source node 20, receiving or addressee or destinationnode 21 and other nodes 22 not involved in the current communication.

Upon starting the backoff process 270 prior to transmitting data, astation e.g. source node 20, initializes its backoff time counter to arandom value as explained above. The backoff time counter is decrementedonce every time slot interval 260 for as long as the radio medium issensed idle (countdown starts from T0, 23 as shown in the Figure).

Channel sensing is for instance performed using Clear-Channel-Assessment(CCA) signal detection which is a WLAN carrier sense mechanisms definedin the IEEE 802.11-2007 standards.

The time unit in the 802.11 standard is the slot time called ‘aSlotTime’parameter. This parameter is specified by the PHY (physical) layer (forexample, aSlotTime is equal to 9 μs for the 802.11n standard). Alldedicated space durations (e.g. backoff) add multiples of this time unitto the SIFS value.

The backoff time counter is ‘frozen’ or suspended when a transmission isdetected on the radio medium channel (countdown is stopped at T1, 24 forother nodes 22 having their backoff time counter decremented).

The countdown of the backoff time counter is resumed or reactivated whenthe radio medium is sensed idle anew, after a DIFS time period. This isthe case for the other nodes at T2, 25 as soon as the transmissionopportunity TXOP granted to source node 20 ends and the DIFS period 28elapses. DIFS 28 (DCF inter-frame space) thus defines the minimumwaiting time for a source node before trying to transmit some data. Inpractice, DIFS=SIFS+2*aSlotTime.

When the backoff time counter reaches zero (26) at T1, the timerexpires, the corresponding node 20 requests access onto the medium inorder to be granted a TXOP, and the backoff time counter isreinitialized 29 using a new random backoff value.

In the example of the Figure implementing the RTS/CTS scheme, at T1, thesource node 20 that wants to transmit data frames 230 sends a specialshort frame or message acting as a medium access request to reserve theradio medium, instead of the data frames themselves, just after thechannel has been sensed idle for a DIFS or after the backoff period asexplained above.

The medium access request is known as a Request-To-Send (RTS) message orframe. The RTS frame generally includes the addresses of the source andreceiving nodes (“destination 21”) and the duration for which the radiomedium is to be reserved for transmitting the control frames (RTS/CTS)and the data frames 230.

Upon receiving the RTS frame and if the radio medium is sensed as beingidle, the receiving node 21 responds, after a SIFS time period 27 (forexample, SIFS is equal to 16 μs for the 802.11n standard), with a mediumaccess response, known as a Clear-To-Send (CTS) frame. The CTS framealso includes the addresses of the source and receiving nodes, andindicates the remaining time required for transmitting the data frames,computed from the time point at which the CTS frame starts to be sent.

The CTS frame is considered by the source node 20 as an acknowledgmentof its request to reserve the shared radio medium for a given timeduration.

Thus, the source node 20 expects to receive a CTS frame 220 from thereceiving node 21 before sending data 230 using unique and unicast (onesource address and one addressee or destination address) frames.

The source node 20 is thus allowed to send the data frames 230 uponcorrectly receiving the CTS frame 220 and after a new SIFS time period27, in a transmission opportunity that is thus granted to it thanks tothe RTS/CTS exchange.

An ACK frame 240 is sent by the receiving node 21 after having correctlyreceived the data frames sent, after a new SIFS time period 27.

If the source node 20 does not receive the ACK 240 within a specifiedACK Timeout (generally within the TXOP), or if it detects thetransmission of a different frame on the radio medium, it reschedulesthe frame transmission using the backoff procedure anew.

Since the RTS/CTS four-way handshaking mechanism 210/220 is optional inthe 802.11 standard, it is possible for the source node 20 to send dataframes 230 immediately upon its backoff time counter reaching zero (i.e.at T1).

The requested time duration for transmission defined in the RTS and CTSframes defines the length of the granted transmission opportunity TXOP,and can be read by any listening node (“other nodes 22” in FIG. 2) inthe radio network.

To do so, each node has in memory a data structure known as the networkallocation vector or NAV to store the time duration for which it isknown that the medium will remain busy. When listening to a controlframe (RTS 210 or CTS 220) not addressed to itself, a listening node 22updates its NAVs (NAV 255 associated with RTS and NAV 250 associatedwith CTS) with the requested transmission time duration specified in thecontrol frame. The listening nodes 22 thus keep in memory the timeduration for which the radio medium will remain busy.

Access to the radio medium for the other nodes 22 is consequentlydeferred 30 by suspending 31 their associated timer and then by laterresuming 32 the timer when the NAV has expired.

This prevents the listening nodes 22 from transmitting any data orcontrol frames during that period.

It is possible that receiving node 21 does not receive RTS frame 210correctly due to a message/frame collision or to fading. Even if it doesreceive it, receiving node 21 may not always respond with a CTS 220because, for example, its NAV is set (i.e. another node has alreadyreserved the medium). In any case, the source node 20 enters into a newbackoff procedure.

The RTS/CTS four-way handshaking mechanism is very efficient in terms ofsystem performance, in particular with regard to large frames since itreduces the length of the messages involved in the contention process.

In detail, assuming perfect channel sensing by each communication node,collision may only occur when two (or more) frames are transmittedwithin the same time slot after a DIFS 28 (DCF inter-frame space) orwhen their own back-off counter has reached zero nearly at the same timeT1. If both source nodes use the RTS/CTS mechanism, this collision canonly occur for the RTS frames. Fortunately, such collision is earlydetected by the source nodes since it is quickly determined that no CTSresponse has been received.

As described above, the original IEEE 802.11 MAC always sends anacknowledgement (ACK) frame 240 after each data frame 230 received.

However, such collisions limit the optimal functioning of the radionetwork. As described above, simultaneous transmission attempts fromvarious wireless nodes lead to collisions. The 802.11 backoff procedurewas first introduced for the DCF mode as the basic solution forcollision avoidance. In the emerging IEEE 802.11n/ac/ax standards, thebackoff procedure is still used as the fundamental approach forsupporting distributed access among mobile stations or nodes.

FIGS. 3a, 3b and 3c illustrate the IEEE 802.11e EDCA involving accesscategories, in order to improve the quality of service (QoS). In theoriginal DCF standard, a communication node includes only onetransmission queue/buffer. However, since a subsequent data frame cannotbe transmitted until the transmission/retransmission of a precedingframe ends, the delay in transmitting/retransmitting the preceding frameprevents the communication from having QoS.

The IEEE 802.11e has overturned this deficiency in providing quality ofservice (QoS) enhancements to make more efficient use of the wirelessmedium.

This standard relies on a coordination function, called hybridcoordination function (HCF), which has two modes of operation: enhanceddistributed channel access (EDCA) and HCF controlled channel access(HCCA).

EDCA enhances or extends functionality of the original access DCFmethod: EDCA has been designed for support of prioritized trafficsimilar to DiffServ (Differentiated Services), which is a protocol forspecifying and controlling network traffic by class so that certaintypes of traffic get precedence.

EDCA is the dominant channel access mechanism in WLANs because itfeatures a distributed and easily deployed mechanism.

The above deficiency of failing to have satisfactory QoS due to delay inframe retransmission has been solved with a plurality of transmissionqueues/buffers.

QoS support in EDCA is achieved with the introduction of four AccessCategories (ACs), and thereby of four corresponding transmission/trafficqueues or buffers (310). Of course, another number of traffic queues maybe contemplated.

Each AC has its own traffic queue/buffer to store corresponding dataframes to be transmitted on the network. The data frames, namely theMSDUs, incoming from an upper layer of the protocol stack are mappedonto one of the four AC queues/buffers and thus input in the mapped ACbuffer.

Each AC has also its own set of channel access parameters or its“backoff parameters”, and is associated with a priority value, thusdefining traffic of higher or lower priority of MSDUs. Thus, there is aplurality of traffic queues for serving data traffic at differentpriorities.

That means that each AC (and corresponding buffer) acts as anindependent DCF contending entity including its respective queue backoffengine 311. Thus, each queue backoff engine 311 is associated with arespective traffic queue for computing a respective queue backoff valueto be used to contend for access to at least one communication channelin order to transmit data stored in the respective traffic queue.

It results that the ACs within the same communication node compete onewith each other to access the wireless medium and to obtain atransmission opportunity, using the contention mechanism as explainedabove with reference to FIG. 2 for example.

Service differentiation between the ACs is achieved by setting differentqueue backoff parameters between the ACs, such as different contentionwindow parameters (CW_(min), CW_(max)), different arbitration interframespaces (AIFS), and different transmission opportunity duration limits(TXOP_Limit).

With EDCA, high priority traffic has a higher chance of being sent thanlow priority traffic: a node with high priority traffic waits a littleless (low CW) before it sends its packet, on average, than a node withlow priority traffic.

The four AC buffers (310) are shown in FIG. 3 a.

Buffers AC3 and AC2 are usually reserved for real-time applications(e.g., voice or video transmission). They have, respectively, thehighest priority and the last-but-one highest priority.

Buffers AC1 and AC0 are reserved for best effort and background traffic.They have, respectively, the last-but-one lowest priority and the lowestpriority.

Each data unit, MSDU, arriving at the MAC layer from an upper layer(e.g. Link layer) with a priority is mapped into an AC according tomapping rules. FIG. 3b shows an example of mapping between eightpriorities of traffic class (User Priorities or UP, 0-7 according IEEE802.1d) and the four ACs. The data frame is then stored in the buffercorresponding to the mapped AC.

When the backoff procedure for a traffic queue (or an AC) ends, the MACcontroller (reference 704 in FIG. 7 below) of the transmitting nodetransmits a data frame from this traffic queue to the physical layer fortransmission onto the wireless communication network.

Since the ACs operate concurrently in accessing the wireless medium, itmay happen that two ACs of the same communication node have theirbackoff ending simultaneously. In such a situation, a virtual collisionhandler (312) of the MAC controller operates a selection of the AChaving the highest priority (as shown in FIG. 3b ) between theconflicting ACs, and gives up transmission of data frames from the ACshaving lower priorities.

Then, the virtual collision handler commands those ACs having lowerpriorities to start again a backoff operation using an increased CWvalue.

FIG. 3c illustrates configurations of a MAC data frame and a QoS controlfield (300) included in the header of the IEEE 802.11e MAC frame.

The MAC data frame also includes, among other fields, a Frame Controlheader (301) and a frame body (302).

As represented in the Figure, the QoS control field 300 is made of twobytes, including the following information items:

-   -   Bits B0 to B3 are used to store a traffic identifier (TID) which        identifies a traffic stream. The traffic identifier takes the        value of the transmission priority value (User Priority UP,        value between 0 and 7—see FIG. 3b ) corresponding to the data        conveyed by the data frame or takes the value of a traffic        stream identifier (TSID, value between 8 and 15) for other data        streams;    -   Bit B4 is set to 1 and is not detailed here;    -   Bits B5 and B6 define the ACK policy subfield which specifies        the acknowledgment policy associated with the data frame. This        subfield is used to determine how the data frame has to be        acknowledged by the receiving node; normal ACK, no ACK or Block        ACK.

“Normal ACK” refers to the case where the transmitting node or sourcenode requires a conventional acknowledgment to be sent (by the receivingnode) for each data frame, after a short interframe space (SIFS) periodfollowing the transmission of the data frame.

“No ACK” refers to the case where the source node does not requireacknowledgment. That means that the receiving node takes no action uponreceipt of the data frame.

“Block ACK” refers to an acknowledgment per block of MSDUs. The BlockAck scheme allows two or more data frames 230 to be transmitted before aBlock ACK frame is returned to acknowledge the receipt of the dataframes. The Block ACK increases communication efficiency since only onesignaling ACK frame is needed to acknowledge a block of frames, whileevery ACK frame originally used has a significant overhead for radiosynchronization. The receiving node takes no action immediately uponreceiving the last data frame, except the action of recording the stateof reception in its scoreboard context. With such a value, the sourcenode is expected to send a Block ACK request (BAR) frame, to which thereceiving node responds using the procedure described below;

Bit B7 is reserved (not used by the current 802.11 standards); and

Bits B8-B15 indicate the amount of buffered traffic for a given TID atthe non-AP station sending this frame. The AP may use this informationto determine the next TXOP duration it will grant to the station. Aqueue size of 0 indicates the absence of any buffered traffic for thatTID.

To meet the ever-increasing demand for faster wireless networks tosupport bandwidth-intensive applications, 802.11ac is targeting largerbandwidth transmission through multi-channel operations. FIG. 4illustrates 802.11ac channel allocation that support composite channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz

IEEE 802.11ac introduces support of a restricted number of predefinedsubsets of 20 MHz channels to form the sole predefined composite channelconfigurations that are available for reservation by any 802.11ac nodeon the wireless network to transmit data.

The predefined subsets are shown in the Figure and correspond to 20 MHz,40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHzand 40 MHz supported by 802.11n. Indeed, the 20 MHz component channels300-1 to 300-8 are concatenated to form wider communication compositechannels.

In the 802.11ac standard, the channels of each predefined 40 MHz, 80 MHzor 160 MHz subset are contiguous within the operating frequency band,i.e. no hole (missing channel) in the composite channel as ordered inthe operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels thatmay or may not be frequency contiguous. The 80 MHz and 40 MHz channelsare respectively composed of two frequency adjacent or contiguous 40 MHzand 20 MHz channels, respectively. However the present invention mayhave embodiments with either composition of the channel bandwidth, i.e.including only contiguous channels or formed of non-contiguous channelswithin the operating band.

A node is granted a TxOP through the enhanced distributed channel access(EDCA) mechanism on the “primary channel” (300-3). Indeed, for eachcomposite channel having a bandwidth, 802.11ac designates one channel as“primary” meaning that it is used for contending for access to thecomposite channel. The primary 20 MHz channel is common to all nodes(STAs) belonging to the same basic set, i.e. managed by or registered tothe same local Access Point (AP).

However, to make sure that no other legacy node (i.e. not belonging tothe same set) uses the secondary channels, it is provided that thecontrol frames (e.g. RTS frame/CTS frame) reserving the compositechannel are duplicated over each 20 MHz channel of such compositechannel.

As addressed earlier, the IEEE 802.11ac standard enables up to four, oreven eight, 20 MHz channels to be bound. Because of the limited numberof channels (19 in the 5 GHz band in Europe), channel saturation becomesproblematic. Indeed, in densely populated areas, the 5 GHz band willsurely tend to saturate even with a 20 or 40 MHz bandwidth usage perWireless-LAN cell.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, one may consider multi-user transmission features,allowing multiple simultaneous transmissions to different users in bothdownlink and uplink directions. In the uplink, multi-user transmissionscan be used to mitigate the collision probability by allowing multiplenodes to simultaneously transmit.

To actually perform such multi-user transmission, it has been proposedto split a granted 20 MHz channel (300-1 to 300-4) into sub-channels 410(elementary sub-channels), also referred to as sub-carriers or resourceunits (RUs), that are shared in the frequency domain by multiple users,based for instance on Orthogonal Frequency Division Multiple Access(OFDMA) technique.

This is illustrated with reference to FIG. 5.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

Contrary to downlink OFDMA wherein the AP can directly send multipledata to multiple stations (supported by specific indications inside thePLOP header), a trigger mechanism has been adopted for the AP to triggeruplink communications from various nodes.

To support an uplink multi-user transmission (during a pre-empted TxOP),the 802.11ax AP has to provide signaling information for both legacystations (non-802.11ax nodes) to set their NAV and for 802.11ax nodes todetermine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11axnodes, meaning 802.11 nodes of previous technologies that do not supportOFDMA communications.

As shown in the example of FIG. 5, the AP sends a trigger frame (TF) 430to the targeted 802.11ax nodes. The bandwidth or width of the targetedcomposite channel is signaled in the TF frame, meaning that the 20, 40,80 or 160 MHz value is added. The TF frame is sent over the primary 20MHz channel and duplicated (replicated) on each other 20 MHz channelsforming the targeted composite channel. As described above for theduplication of control frames, it is expected that every nearby legacynode (non-HT or 802.11ac nodes) receiving the TF on its primary channel,then sets its NAV to the value specified in the TF frame in order. Thisprevents these legacy nodes from accessing the channels of the targetedcomposite channel during the TXOP.

Based on an AP's decision, the trigger frame TF may define a pluralityof resource units (RUs) 410, or “Random RUs”, which can be randomlyaccessed by the nodes of the network. In other words, Random RUsdesignated or allocated by the AP in the TF may serve as basis forcontention between nodes willing to access the communication medium forsending data. A collision occurs when two or more nodes attempt totransmit at the same time over the same RU.

A trigger frame that can be randomly accessed is referred to as atrigger frame for random access (TF-R). A TF-R may be emitted by the APto allow multiple nodes to perform UL MU (UpLink Multi-User) randomaccess to obtain an RU for their UL transmissions.

The trigger frame TF may also designate Scheduled resource units, inaddition or in replacement of the Random RUs. Scheduled RUs may bereserved by the AP for certain nodes in which case no contention foraccessing such RUs is needed for these nodes. Such RUs and theircorresponding scheduled nodes are indicated in the trigger frame. Forinstance, a node identifier, such as the Association ID (AID) assignedto each node upon registration, is added in association with eachScheduled RU in order to explicitly indicate the node that is allowed touse each Scheduled RU.

An AID equal to 0 may be used to identify random RUs.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

Also the AP may assign Random RUs to a specific group of nodes, whichthus compete for contending for access to these Random RUs. Forinstance, the AP may specify a node group ID, such as a BSSID (standingfor “Basic Service Set Identification”) in case the AP handles aplurality of BSSs.

In the example of FIG. 5, each 20 MHz channel (400-1, 400-2, 400-3 or400-4) is sub-divided in frequency domain into four sub-channels or RUs410, typically of size 5 Mhz.

Of course the number of RUs splitting a 20 MHz channel may be differentfrom four. For instance, between two to nine RUs may be provided (thuseach having a size between 10 MHz and about 2 MHz).

Once the nodes have used the RUs to transmit data to the AP, the APresponds with an acknowledgment (not show in the Figure) to acknowledgethe data on each RU.

Document IEEE 802.11-15/1105 provides an exemplary random allocationprocedure that may be used by the nodes to access the Random RUsindicated in the TF. This random allocation procedure is based on a newbackoff counter, referred below to as the OFDMA or RU backoff value (orOBO), inside the 802.11ax nodes for allowing a dedicated contention whenaccessing an RU to send data.

The OFDMA backoff value OBO to contend for access to the random RUs israndomly selected within the contention window range [0, CWO] whereinCWO is the contention window size and is defined in a selection range[CWO_(min), CWO_(max)].

The RU backoff counter may for instance be the same as a conventionalbackoff counter, i.e. be a simple copy thereof.

Each node STA1 to STAn is a transmitting node with regards to receivingAP, and as a consequence, each node has an active RU backoff engineseparate from the one or more queue backoff engines, for computing an RUbackoff value (OBO) to be used to contend for access to at least onerandom resource unit splitting a transmission opportunity granted on thecommunication channel, in order to transmit data stored in one or eithertraffic queue AC.

Below RU backoff and OBO backoff are synonymous and refer to the samebackoff engine used to contend for access to the Random RUs.

The random allocation procedure comprises, for a node of a plurality ofnodes having an active RU backoff value OBO, a first step of determiningfrom the trigger frame the sub-channels or RUs of the communicationmedium available for contention, a second step of verifying if the valueof the active RU backoff value OBO local to the considered node is notgreater than a number of detected-as-available random RUs, and then, incase of successful verification, a third step of randomly selecting a RUamong the detected-as-available RUs for sending data. In case of secondstep is not verified, a fourth step (instead of the third) is performedin order to decrement the RU backoff value OBO by the number ofdetected-as-available RUs.

As shown in the Figure, some Resource Units may not be used (410 u)because no node with an RU backoff value OBO less than the number ofavailable random RUs has randomly selected one of these RUs, whereassome other are collided (as example 410 c) because two of these nodeshave randomly selected the same RU.

The conventional handling of random RUs is not satisfactory. There is aneed to provide fair use of the network in dense wireless environmentswith more efficient allocation schemes used to allocate the OFDMA RUs tothe nodes.

Few allocation schemes are known in the prior art. For instance, thepublication “Generalized CSMA/CA for OFDMA Systems” (Hojoong Kwon et al.[IEEE GLOBECOM 2008, ISBN 978-1-4244-2324-8]) proposed a CSMA/CAprotocol for OFDMA systems providing a random access scheme based onbackoff mechanism.

Unfortunately, the proposed scheme is not compliant with theconventional 802.11 random access. In particular, this is because theproposed scheme does not keep considering the 20 MHz channel as the maincommunication entity to allocate to the nodes. Furthermore, the use ofthe RUs is not optimum: as a random access, some collisions may occur onsome RUs and some other RUs may remain empty or unused even if somenodes have data to transmit (because their associated backoff is notequal to zero).

More appropriate setting and updating of parameters for managing the RUbackoff engine is proposed to be used in some improvements according tothe invention. An idea of these improvements is to determine one or moreRU backoff parameters based on one or more queue backoff parameters ofthe queue backoff engines; and then to compute the RU backoff value fromthe determined one or more RU backoff parameters. This approach may thustake into account the prioritization of un-managed traffic towards theAP to improve the management of the RU backoff parameters with regardsto the pending traffic.

Also the coexistence of OFDMA (or RU) backoff scheme, when implemented,and EDCA queue backoff scheme for CSMA/CA contention may make thehandling of Random RUs more difficult.

Other improvements according to the present invention provide improvedwireless communications with more efficient use of the OFDMA Random RUswhile limiting the risks of collisions on these RUs. All of this ispreferably kept compliant with 802.11 standards.

An exemplary wireless network is an IEEE 802.11ac network (and upperversions). However, embodiments of the invention apply to any wirelessnetwork comprising an access point AP 110 and a plurality of nodes101-107 transmitting data to the AP through a multi-user transmission.Embodiments of the invention are especially suitable for datatransmission in an IEEE 802.11ax network (and future versions) requiringbetter use of bandwidth.

An exemplary management of multi-user transmission in such a network hasbeen described above with reference to FIGS. 1 to 4.

First embodiments of first improvements according to the inventionprovide a dynamic control by the AP of parameters used by the nodes tocontend for access to the Random RUs. Following one or more triggerframes reserving one or more transmission opportunities on at least onecommunication channel of the wireless network, each trigger framedefining resource units forming the communication channel and includinga plurality of random resource units that the nodes access using acontention scheme, the wireless communication method according to thefirst embodiments has specific steps.

At the access point AP, they include:

determining statistics on random resource units not used by the nodesduring the one or more transmission opportunities and/or random resourceunits on which nodes collide during the one or more transmissionopportunities;

determining a correcting or “TBD” parameter based on the determinedstatistics,

sending, to the nodes, a next trigger frame for reserving a nexttransmission opportunity, the next trigger frame including thedetermined TBD parameter.

At the nodes, they include:

determining, based on the received TBD parameter and on one randomparameter local to the node, one of the random resource units (this stepcorresponds to the way the nodes contend for access to the randomresource units according to the first embodiments of the invention);

transmitting data to the access point using the determined randomresource unit.

All of this shows that a correcting or TBD parameter is exchangedbetween the access point and the nodes. On one hand, it is used by thenodes to adjust how the local random parameter impacts the choice of therandom RUs to be used. On the other hand, this TBD parameter iscalculated by the access point based on statistics related to the use ofthe Random RUs (unused or collided RUs) in one or more previoustransmission opportunities. This is because the access point has anoverall view of the network, as the nodes only communicate with it.

It results that the contention scheme used by the nodes to access theRandom RUs can be dynamically adapted to the network environment. As aconsequence, more efficient usage of the network bandwidth (of the RUs)with limited risks of collisions can be achieved.

Second embodiments of the first improvements provide a progressivecontention scheme in the nodes for access to the Random RUs. Following atrigger frame reserving a transmission opportunity on at least onecommunication channel of the wireless network, the trigger framedefining resource units forming the communication channel including aplurality of random resource units that the nodes access using acontention scheme, the wireless communication method according to thesecond embodiments has specific steps.

At the nodes (not the AP), they include:

determining a first time instant based on one random parameter local tothe node;

sending padding (or dummy) data on a first one of the random resourceunits from the determined first time instant up to the end of apredetermined time window after having received the trigger frame (thedetermining and sending steps thus forming a mechanism for contendingfor access to the RUs according to embodiments of the invention);

starting transmitting data to the access point on the first randomresource unit when the predetermined time window ends (it defines apredefined second time instant).

This new contention mechanism particularly applies to OFDMA RUs. This isbecause, due to synchronization requirements between the OFDM symbols,the nodes implementing the second embodiments of the invention only sendpadding data. The padding data are sent up to a time point (predefinedsecond time instant) at which all the nodes having data to transmitsimultaneously start transmitting the data. Synchronization is thussaved, while having an efficient contention scheme to access the RandomRUs.

Note that the nodes being allocated with a respective Scheduled RU inthe communication channel should also wait for the end of the timewindow before transmitting their data. “Wait” may also mean sendingpadding data on the Scheduled RU.

The first and second embodiments can be implemented separately, or incombination as further described below to provide a progressivecontention mechanism with dynamic adaptation to the network conditions.

Second improvements according to the invention provide a self-control ofthe nodes for accessing the Random RUs, using an RU backoff valuecomputed by an RU backoff engine. Following a trigger frame reserving atransmission opportunity on at least one communication channel of thewireless network, the trigger frame defining resource units forming thecommunication channel including a plurality of random resource unitsthat the nodes access using a contention scheme, the wirelesscommunication method according to the second improvements has specificsteps at one of the nodes.

Based on a current RU backoff value, the node accesses a random resourceunit to transmit data to the access point; and after having transmittedthe data, the node computes a new RU backoff value to contend for newaccess to random resource units (e.g. in a next trigger frame). The RUbackoff value is a value randomly selected within a contention windowrange defined by a contention window size, and the contention windowsize CWO is updated depending on a success or failure in transmittingthe data.

As described below, an approach for the second improvements is to doublethe contention window size CWO in case of transmission failure.

This approach restricts transmissions in case of collisions, which inturn reduces the probability of collisions and thus improves use of thecommunication network.

The above first and second improvements show two modes to drive thevalue CWO defining the contention window size at the node, in order tocontrol the RU backoff value OBO and thus the access to the random RUs :the first improvements refer to an AP-initiated mode in which the accesspoint sends a correcting parameter, noted below TBD parameter, to thenodes to drive them in defining their own contention window size; in thesecond improvements, each node is autonomous on computing its owncontention window size CWO through a fully local mode.

The inventors have noticed that the relative efficiency between thesetwo modes can change depending on network conditions, such as the numberof available random RUs or the number of nodes competing for accessingthe random RUs.

FIG. 22 illustrates simulation curves of the evolution of a random-RUuse efficiency metric depending on the number of the competing nodes.One may note that in some network configurations, the fully local modeis more efficient than the AP-initiated mode, and that in other networkconfigurations, the balance of efficiency is reversed.

In this context, the invention also provides a way to efficiently switchbetween the two modes in order to obtain more efficient usage of thenetwork bandwidth (of the RUs) with limited risks of collisions. To doso, the access point may:

determining use statistics on the use of the random resource units bythe nodes during the one or more transmission opportunities;

determine, based on the determined use statistics, a TBD parameter todrive nodes in defining their own contention window size;

evaluate a measure of use efficiency of the random resource units basedon the determined use statistics; and

deciding, based on the evaluated use efficiency measure, to transmit ornot, to the nodes, the determined TBD parameter within a next triggerframe for reserving a next transmission opportunity.

Correspondingly, any node may:

determine whether or not the received trigger frame includes a TBDparameter to drive the node in defining its own contention window size;

in case of positive determining, compute a new contention window sizebased on the received TBD parameter; otherwise, use a local contentionwindow size as new contention window size, to contend for access to therandom resource units splitting the transmission opportunity; and then

transmit data to the access point upon accessing one of the randomresource units.

The controlled switch between the two modes for computing CWO at thenodes thus takes advantage of an overall analysis by the access point(through the TBD parameter) or of specificities local to each node,depending on which may provide the better use of the random RUs. Thecontrolled switch dynamically adapts thanks to an analysis of usestatistics on the use of the random RUs of the one or more transmissionopportunities reserved by the one or more trigger frames.

As a consequence, the nodes dynamically adapt the computation of theircontention window sizes, as they receive or not the TBD parameter.

FIG. 6 schematically illustrates a communication device 600 of the radionetwork 100, configured to implement at least one embodiment of thepresent invention. The communication device 600 may preferably be adevice such as a micro-computer, a workstation or a light portabledevice. The communication device 600 comprises a communication bus 613to which there are preferably connected:

-   -   a central processing unit 611, such as a microprocessor, denoted        CPU;    -   a read only memory 607, denoted ROM, for storing computer        programs for implementing the invention;    -   a random access memory 612, denoted RAM, for storing the        executable code of methods according to embodiments of the        invention as well as the registers adapted to record variables        and parameters necessary for implementing methods according to        embodiments of the invention; and    -   at least one communication interface 602 connected to the radio        communication network 100 over which digital data packets or        frames or control frames are transmitted, for example a wireless        communication network according to the 802.11ax protocol. The        frames are written from a FIFO sending memory in RAM 612 to the        network interface for transmission or are read from the network        interface for reception and writing into a FIFO receiving memory        in RAM 612 under the control of a software application running        in the CPU 611.

Optionally, the communication device 600 may also include the followingcomponents:

-   -   a data storage means 604 such as a hard disk, for storing        computer programs for implementing methods according to one or        more embodiments of the invention;    -   a disk drive 605 for a disk 606, the disk drive being adapted to        read data from the disk 606 or to write data onto said disk;    -   a screen 609 for displaying decoded data and/or serving as a        graphical interface with the user, by means of a keyboard 610 or        any other pointing means.

The communication device 600 may be optionally connected to variousperipherals, such as for example a digital camera 608, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 600.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 600 or connected to it. The representation of thebus is not limiting and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 600 directly or by means of another element of the communicationdevice 600.

The disk 606 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to the invention to be implemented.

The executable code may optionally be stored either in read only memory607, on the hard disk 604 or on a removable digital medium such as forexample a disk 606 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 603, via the interface 602, in order to bestored in one of the storage means of the communication device 600, suchas the hard disk 604, before being executed.

The central processing unit 611 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 604 or in the read only memory 607, aretransferred into the random access memory 612, which then contains theexecutable code of the program or programs, as well as registers forstoring the variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 7 is a block diagram schematically illustrating the architecture ofa communication device or node 600, either the AP 110 or one of nodes100-107, adapted to carry out, at least partially, the invention. Asillustrated, node 600 comprises a physical (PHY) layer block 703, a MAClayer block 702, and an application layer block 701.

The PHY layer block 703 (here an 802.11 standardized PHY layer) has thetask of formatting, modulating on or demodulating from any 20 MHzchannel or the composite channel, and thus sending or receiving framesover the radio medium used 100, such as 802.11 frames, for instancemedium access trigger frames TF 430 to reserve a transmission slot, MACdata and management frames based on a 20 MHz width to interact withlegacy 802.11 stations, as well as of MAC data frames of OFDMA typehaving smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/fromthat radio medium.

The MAC layer block or controller 702 preferably comprises a MAC 802.11layer 704 implementing conventional 802.11ax MAC operations, and anadditional block 705 for carrying out, at least partially, theinvention. The MAC layer block 702 may optionally be implemented insoftware, which software is loaded into RAM 512 and executed by CPU 511.

Preferably, the additional block, referred as to random RU proceduremodule 705 for controlling access to OFDMA resource units(sub-channels), implements the part of the invention that regards node600, i.e. transmitting operations for a source node, receivingoperations for a receiving node, or operations for the AP.

For instance and not exhaustively, the operations for the AP may includegathering statistics on use of the Random RUs, computing a correcting“TBD” parameter and optionally a time window size, adjusting the numberof Random RUs; the operations for a node different from the AP mayinclude using such information from the AP to compute a contentionwindow size and thus to contend for access to the RUs, calculating alocal RU backoff value for such contention, sensing use or not of theRandom RUs before accessing one of them, at the nodes.

MAC 802.11 layer 704 and random RU procedure module 705 interact onewith the other in order to provide management of the queue backoffengines and RU backoff engines.

On top of the Figure, application layer block 701 runs an applicationthat generates and receives data packets, for example data packets of avideo stream. Application layer block 701 represents all the stacklayers above MAC layer according to ISO standardization.

Embodiments of the present invention are now illustrated using variousexemplary embodiments. Although the proposed examples use the triggerframe 430 (see FIG. 5a ) sent by an AP for a multi-user uplinktransmissions, equivalent mechanisms can be used in a centralized or inan adhoc environment (i.e. without an AP).

First and second embodiments of first improvements are illustrated fromthe nodes' perspective through FIG. 8 and from the AP's perspectivethrough FIG. 11. In these exemplary embodiments, the trigger frameincludes a correcting or TBD parameter used to optimize the OFDMA RandomRUs allocation for the next OFDMA TXOP.

FIG. 8a illustrates, using a flowchart, general steps of a wirelesscommunication method at one of the nodes (not the AP) according to afirst exemplary embodiment of the invention. In this first exemplaryembodiment, the random resource units (Random RUs) have respectiveunique indexes (for instance an ordering index), and the correctingparameter TBD is applied to a local random parameter to obtain a result,the result identifying the index of the random resource unit to be usedby the node to transmit the data to the access point.

In this example, the random parameter local to the node is based on theconventional backoff value (or counter) of the node used to contend foraccess to the communication channel (i.e. a value corresponding to thenumber of time-slots the node waits before accessing the communicationmedium).

In other words, the correcting parameter TBD is used (with the localbackoff counter) to allocate the Random RUs.

Upon receiving of a trigger frame from the AP (710), the node STAextracts the correcting parameter TBD value and the number of RUssubject to random allocation, from the trigger frame.

By default, a transmitting 802.11 node has its own (local) backoffcounter different from zero (otherwise it would have accessed themedium).

In this first exemplary embodiment, the transmitting node computes amultichannel backoff value (i.e. a local random parameter or OBO forOFDMA BackOff counter) based on the current value of the standard 802.11backoff counter value and based on the extracted correcting parameterTBD value. This is step 711.

For instance, to speed up the backoff decrement over time as explainedbelow (step 712) and to tend to allocate all the Random RUs, the localmultichannel backoff value OBO may be equal to the standard 802.11backoff value divided by the correcting parameter TBD value. A roundingoperation is used to obtain an integer, if appropriate. This approachcan be implemented in a simple way, which is particularly adapted to lowresource nodes.

Of course, operations other than a division (e.g. multiplication, morecomplex mathematical functions) may be used, and the TBD parameter sentby the AP can be adapted to the operation used by the nodes.

To increase the number of nodes (i.e. multichannel backoff values) thatcan access the Random RUs, all the multichannel backoff values OBO belowa predefined threshold (for instance N×M where N is an integer and M isthe number of Random RUs) can be kept and a modulo M operation can beapplied to them in order to map each kept multichannel backoff value OBOon one of the Random RUs. Depending on the network conditions, thisapproach may increase the risk of collisions on the Random RUs.

Once the local multichannel backoff value OBO has been computed, step712 consists for the node to determine whether or not it is selected forcontenting on a random RU.

One solution for the selection of contenting nodes is to compare thelocal multichannel backoff value OBO with the number of RUs to beallocated. For instance, when the number of RUs to be allocated is 8 (asan example, a 40 MHz band, wherein each 20 MHz channel band contains 4OFDMA RUs), all the transmitting nodes with a local multichannel backoffvalue OBO less than 8 are considered as eligible for having access ontoa Random RU. On the other hand, the other transmitting nodes are notselected for Random RU allocation in the current TXOP and must wait foranother transmission opportunity (OFDMA TXOP or standard TXOP) beforesending their data.

Next step is step 713 in which the node selects the Random RU to beused. In this exemplary embodiment, the Random RU having an index equalto the local multichannel backoff value OBO computed at step 712 isselected.

Next, at step 714, the node transmits at least one 802.11 PPDU frame ina 802.11ax format in the selected Random RU.

Then, it waits for an acknowledgment of the transmitted PPDU frame fromthe AP. This is step 715.

This exemplary embodiment is illustrated through FIG. 9.

FIG. 9 illustrates exemplary communication lines according to suchexemplary random allocation procedure that is used by the nodes toaccess the Random RUs indicated in the TF. As explained above, thisrandom allocation procedure is based on the reuse of the conventionalbackoff counter values of the nodes for assigning an RU to a node of thenetwork to send data.

An AP sends a trigger frame TF defining RUs with random access andincluding the TBD parameter. In the example of the Figure, eight RUswith the same bandwidth are defined for a 40 MHz composite channel, andthe TF 430 is duplicated on the two 20 MHz channels forming thecomposite channel. In other words, the network is configured to handlefour OFDMA Resource Units per each 20 MHz channel.

Each node STA1 to STAn is a transmitting node with regards to receivingAP, and as a consequence, each node has at least one active 802.11backoff value (800), based on which it computes the local multichannelbackoff value (801), using the TBD parameter (802). TBD=2 in thisexample. For instance, node STA2 has an 802.11 backoff value equal to 6,and using TBD=2, it obtains a local multichannel backoff value equal to3.

The random allocation procedure 810 of FIG. 9 comprises, for a node of aplurality of nodes having an active backoff and calculating a localmultichannel backoff value OBO using the TBD parameter specified in theTF, a first step of determining from the trigger frame the Randomsub-channels or RUs of the communication medium available forcontention, a second step of verifying if the value of the multichannelbackoff value local OBO to the considered node is not greater than thenumber of detected-as-available Random RUs, and then a step of sendingdata is performed on the RU whom number equals the local multichannelbackoff value OBO.

In other words, the Random RUs may be indexed in the TF, and each nodeuses the RUs having an index equal to the local multichannel backoffvalue OBO of the node.

As shown in the Figure, some Random Resource Units may not be used, forinstance RUs indexed 2 (410-2), 5, 7 and 8. This is due to therandomization process, and in the present example, due to the fact thatnone of the nodes has a backoff value OBO equal to 2, 5, 7 or 8 afterthe TF has been sent.

To base the Random RU allocation on the conventional 802.11 backoffvalue allows maintaining the access priority defined in the 802.11standard. Another advantage is that the Random RU allocation keeprelying on classical random generation resources present in conventional802.11 hardware.

While the above example selects the Random RUs based on its RU indexmatching the local multichannel backoff value OBO, other approaches, forinstance selecting randomly the Random RU, can be implemented. In anycase, the overall allocation is randomized since the local multichannelbackoff value OBO is intrinsically randomly computed.

FIG. 8b illustrates, using a flowchart, general steps of a wirelesscommunication method at one of the nodes (not the AP) according to asecond exemplary embodiment of the invention. In this second exemplaryembodiment, the AP defines a time window size, denoted ΔT (specified inthe TF), in which the nodes can perform contention on the Random RUs.Once the time window ends, all the nodes to which a RU has beenallocated (thus including the Scheduled RUs) start transmitting theirdata simultaneously. This is to keep OFDMA synchronization between thenodes.

As an alternative to an explicit indication in the TF, the time windowsize may be determined locally on each node using the same determinationscheme.

Upon receiving a trigger frame from the AP (720), the node STA extracts,from the trigger frame, the TBD parameter value, the ΔT period and thenumber of RUs subject to random allocation.

By default, a transmitting 802.11 node has its own (local) backoffcounter different from zero (otherwise it would have access the primary20 MHz channel).

In this second exemplary embodiment, the transmitting node computes amultichannel backoff value OBO (i.e. a local random parameter) based onthe current value of the standard 802.11 backoff counter value and basedon the extracted TBD parameter value. This is step 721.

For instance, to speed up the backoff decrement over time as explainedabove (step 702) and to tend to allocate all the Random RUs, the localmultichannel backoff value OBO may be equal to the standard 802.11backoff value divided by the TBD parameter value. A rounding operationis used to obtain an integer, if appropriate. This approach can beimplemented in a simple way, which is particularly adapted to lowresource nodes.

Other variants as described above with reference to FIG. 8a may also beimplemented. In addition, the standard 802.11 backoff value may also beused as the local multichannel backoff value OBO when the contentionscheme of FIG. 8b is implemented.

Upon reception of the trigger frame, after a SIFS time, the localmultichannel backoff OBO is decremented by one at each multichannelbackoff time interval (typically the 802.11ax standard value: 9 μs)during the ΔT period. This is the loop 722-740-output ‘no’ at 741.

Through this loop, as long as the medium is sensed as idle on RandomRUs, the local multichannel backoff value OBO is counted down until itgoes to 0 (test 741). This makes it possible to determine a first timeinstant based on the random parameter local to the node (i.e. the localmultichannel backoff value OBO).

At each multichannel backoff time interval, if the multichannel backoffOBO of the STA is not equal to 0 (test 741), the RU distribution isanalysed. It means that the node continuously senses the use of therandom resource units during the time window. This is step 723.

If a new Random RU is sensed as busy during the current time interval(test 750), the local multichannel backoff value OBO may be updated atstep 751. This is to speed up the RU allocation for the remaining time.

The local multichannel backoff value OBO may be updated based on atleast one correcting parameter specified in the trigger frame receivedfrom the access point, for instance the TBD parameter defined above. Forinstance, the starting formula to compute the local multichannel backoffvalue OBO may be applied again on the current local multichannel backoffvalue: new local multichannel backoff value OBO =current multichannelbackoff/TBD value. Of course, other embodiments may be used.

Steps 750-751 are optional. If they are not implemented, the loop fromoutput ‘no’ at step 741 directly goes to step 722.

During the countdown of the local multichannel backoff value OBO, it isdetermined whether or not at least one Random RU is still available.This is step 724. Indeed, as soon as all the random resource units ofthe at least one communication channel are sensed as used, the node maystop the process of sensing the use of the Random RUs and of countingdown its local multichannel backoff value OBO. This is to avoid uselessprocessing as soon as no further Random RU is available.

In the example of the Figure, upon detecting all the Random RUs areused, the process goes to optional step 730.

If the local multichannel backoff value OBO does not reach zero at theend of the time window ΔT (the ΔT period expires—test 722), no randomresource unit is selected for the node within the transmissionopportunity. The process thus goes to optional step 730.

As no Random RU has been allocated to the node after expiry of ΔT periodor if all Random RUs have been allocated, the node comes back toconventional 802.11 contention for access to the network. At step 730,the 802.11 standard backoff value is set to the current localmultichannel backoff value OBO, i.e. to the value taken by the localrandom parameter at said first time instant. This is to speed up accessto the network for the node, since a number of other nodes with lowerbackoff values have already accessed the network during the ΔT period.Next to step 730, the process ends.

Back to test 741, if the local multichannel backoff value OBO of thenode reaches zero, a first time instant has thus been determined. Atthis time instant, a Random RU is selected and allocated to the node atstep 760.

In particular a Random RU is selected from the available Random RUs. Inother words, one of the random resource units sensed as unused isselected.

In embodiments, the selection can be controlled by using the firstavailable Random RUs. In these embodiments, the random resource unitsare ordered within the communication channel (they have respectiveunique indexes), and the selected unused random resource unit is thefirst one of the sensed unused random resource units according to theorder.

Next to step 760, the node starts sending padding data on the selectedrandom resource unit, at step 761. In particular it sends the paddingdata from the determined first time instant up to the end of apredetermined time window ΔT (loop 762). Sending dummy data (i.e.padding) in the selected Random RU ensures this RU is sensed as busy byother nodes.

Note that the dummy/padding data are sent by the nodes on the allocatedRandom RUs to ensure the OFDM symbol to be synchronized between thetransmitting nodes. This requires that the same padding is alsoperformed for any Scheduled RU in the composite channel forming theTXOP.

At the end of the ΔT period (test 762), the node stops sending paddingdata and starting transmitting data to the access point on the selectedrandom resource unit. At step 763, the node thus sends at least one realdata 802.11 PPDU frame during the OFDMA TXOP in an 802.11ax format inthe selected RU.

Preferably, when the node ends sending the data intended to the accesspoint, the node may continue emitting a signal, for instance by sendingnew padding data, on the selected RU until the end of the TXOP. This isto ensure a correct energy level to be detected by legacy node on the 20MHz channel including the selected RU.

Next at step 764, the node waits for an acknowledgment response from theAP before the next data transmission TXOP.

The process then ends.

This exemplary embodiment is illustrated through FIG. 10.

The 802.11 backoff values 800 are converted into local multichannelbackoff values OBO 801 using TBD parameter 802 as explained above.

From a SIFS after the TF 430, the countdown of the local multichannelbackoff values OBO starts, for the ΔT period.

The first node having a local multichannel backoff value OBO reachingzero (at time t1) is allocated the first Random RU (#1), on which itstarts sending padding data (810). This is STA2.

Next a second node, STA3, has its local multichannel backoff value OBOreaching zero at t2. It then selects the second Random RU (#2, firstavailable one), on which it starts sending padding data (811).

The countdown is performed during the whole ΔT period. In the example ofthe Figure, a third node, STAn, has its local multichannel backoff valueOBO reaching zero before the end of the ΔT period, at t3. It thenselects the third Random RU (#3, first available one), on which itstarts sending padding data (812).

At the end of the ΔT period, nodes STA1 and STAn-1 have non-zero localmultichannel backoff values OBO: they are not allocated with a RandomRUs.

Simultaneously, STA2, STA3 and STAn start transmitting their data usingOFDMA on their respective selected Random RU. They send data up to theend of the TXOP (possibly using padding data if necessary). An ACK thenfollows, sent by the AP.

Turning now to the operations performed by the access point, FIG. 11illustrates, using a flowchart, general steps of a wirelesscommunication method at the AP adapted to the first and/or secondexemplary embodiments introduced above.

One skilled in the art will unambiguously identify which parts of FIG.11 are required for the first exemplary embodiments of FIG. 8a and whichparts of FIG. 11 are required for the second exemplary embodiments ofFIG. 8b . In particular, the AP is configured to compute, update andsend the TBD parameter used to optimize the OFDMA Random RU allocationfor the next OFDMA TXOP in the first exemplary embodiments, and tocompute, update and send the ΔT value in some embodiments of the secondexemplary embodiments. In any case, such information is encapsulatedinside a new Trigger Frame (TF) sent by the AP.

Upon receiving an uplink OFDMA frame (851), the AP is in charge ofsending an acknowledgment frame to acknowledge safe reception oftransmitted data by all or part of the nodes over the OFDMA RUs (852).

At step 853, the AP analyses the number of collided and empty (i.e.unused) OFDMA RUs. It may perform this step by sensing each RU formingthe composite channel. These values are used to update OFDMA statistics.In particular, the AP determines statistics on random resource units notused by the nodes during the transmission opportunity and/or randomresource units on which nodes collide during the transmissionopportunity.

The OFDMA statistics are used by the AP at steps 854-856 to determinevarious parameters to dynamically adapt (from one TXOP to the other) thecontention scheme for access to the Random RUs.

It includes determining the TBD parameter for the next OFDMAtransmission (854) at least for the first exemplary embodiments.

It may also include determining and thus modifying the number of randomresource units within the communication channel for the nexttransmission opportunity (855).

It also includes determining the size of the ΔT period (856).

For the first exemplary embodiments of FIG. 8a , steps 854-855 thusdynamically adapt (from one TXOP to the other) the contention scheme foraccess to the Random RUs, by both adjusting the TBD parameter and thenumber of Random RUs available to the nodes.

To illustrate such dynamical adaptation, it may be considered the casewhere all (or more than 80%) OFDMA Random RUs are used in the last OFDMATXOP (or N previous OFMDA TXOPs, N being integer). It means that manynodes are requesting to transmit data. As a consequence, the number ofRandom RUs for the next OFDMA transmission can be increased by the AP(for instance by 1 up to a maximum number), while the TBD parameter canremain the same.

In addition, if collisions occur on several used OFDMA Random RUs (atleast for instance more than a third), it means that the TBD parametershould be decreased to minimize the collisions between the nodes duringthe RU allocation. For instance, the TBD parameter may be decreased byabout 30%.

A drawback of decreasing the TBD parameter (used as a divisor of the802.11 backoff value by the nodes) is that the Random RU allocation isless optimized.

On the other hand, if several OFDMA Random RUs remain unused (at leastfor instance more than a third—or less than 50% of the RUs are used),the TBD parameter can be increased, for instance by 30%, and/or thenumber of Random RUs for the next OFDMA transmission can be decreased bythe AP (for instance by 1) to optimize the OFDMA Random RU allocation.

A drawback of increasing the TBD parameter is that the collisions duringthe Random RU allocation may increase.

This illustrates that, upon termination of each uplink OFDMA TXOP, theupdating of the TBD parameter is a trade-off between minimizingcollisions during Random RU allocation and optimizing the filling of theOFDMA Random RUs.

To be precise, at step 854, the AP computes a new TBD parameter based onthe determined OFDMA statistics, optionally further based on the numberof nodes transmitting on the random resource units during the previoustransmission opportunity. Note that the OFDMA statistics may bestatistics on the previous TXOP only or on N (integer) previous TXOPs.

For instance, as introduced in the first embodiments of FIG. 8a , theTBD parameter includes a value to apply to a random parameter local toeach node, for the node to determine which one of the random resourceunits to access. For instance, the random parameter can be based on abackoff value used by the node to contend for access to thecommunication channel.

In embodiments, a good starting value for the TBD parameter is 2 (usedas a divisor of the 802.11 backoff value by the nodes). This valuesubstantially increases the speed of the backoff counter, with limitedrisk of addition collisions.

However this value can be adjusted as the OFDMA statistics show that toomany collisions occur on the Random RUs or too many Random RUs remainunused.

Next, at step 855, the AP determines the number of Random RUs toconsider for the next multi-user TXOP about to be granted (because theAP can pre-empt the wireless medium over the nodes, since it must waitfor the medium to be idle during a shorter duration than the waitingduration applied by the nodes).

The determination of step 855 can based on the BSS configurationenvironment, that is to say the basic operational width (namely 20 MHz,40 MHz, 80 MHz or 160 MHz composite channels that include the primary 20MHz channel according to the 802.11ac standard).

For the sake of simplicity, one may consider that a fixed number ofOFDMA RUs is allocated per 20 MHz band by the 802.11ax standard: in thatcase, it is sufficient that the Bandwidth signaling is added to the TFframes (i.e. 20, 40, 80 or 160 MHz values is added). Typically, suchinformation is signaled in the SERVICE field of the DATA section ofnon-HT frames according the 802.11 standard. As a consequence,compliance with 802.11 is kept for the medium access mechanism.

For the second exemplary embodiments of FIG. 8b , step 856 dynamicallyadapts the ΔT value to the network conditions. This adaptation may thusbe based on the OFDMA statistics, i.e. on the number of random resourceunits not used by the nodes during one or more previous transmissionopportunities and/or of random resource units on which nodes collideduring one or more previous transmission opportunities. It is alsoadjusted based on the number of available Random RUs provided in theTXOP.

For instance, the ΔT value is computed as a multiple of the multichannelbackoff time interval (used by the nodes when decrementing their localmultichannel backoff values OBO—equal to 9 μs). As an example, themultiplicity may be equal to the number of available Random RUs(determined at step 855 for the next TXOP). Generally, one can considerthe following equation:

ΔT=(number of available Random RUs×elementary 9 μs time unit)*k

wherein k is an adjusting parameter function of the OFDMA statistics.

Typically ‘k’ value can be set to 2. Its minimum value is 1 to allow theallocation of one Random RU at least at each backoff decrement (9 μs).

The ‘k’ value can be adjusted depending on the number of empty RandomRUs on the past OFDMA TXOP: for instance, if a third of the Random RUsremain unused in the last OFDMA TXOP, the ‘k’ value may be increased by30%.

However, the ΔT value is kept below a predefined threshold, in order toavoid having it too high. This is to avoid spending too much time forthe Random RU allocation.

Next to step 856, steps 857/858 consist for the AP to build and send thenext trigger frame with the above determined information: Random RUsinformation, TBD parameter value, ΔT value.

It is expected that every nearby node (legacy or 802.11ac, i.e. which isneither STA1 nor STA2) can receive the TF on its primary channel. Eachof these nodes then sets its NAV to the value specified in the TF frame:the medium is thus reserved by the AP.

FIG. 12 illustrates an exemplary format for an information Elementdedicated to the transmission of the TBD parameter and/or the ΔT valuewithin the TF. The ‘TBD Information Element’ (1610) is used by the AP toembed additional information within the trigger frame TF related to theOFDMA TXOP.

The proposed format follows the ‘Vendor Specific information element’format as defined in IEEE 802.11-2007 standard.

The ‘TBD Information Element’ (1610) is a container of the TBD parameterattributes (1620), having each a dedicated attribute ID foridentification. The header of TBD Information Element can bestandardized (and thus easily identified by stations 600) through theElement ID.

The TBD attributes 1620 are defined to have a common general formatconsisting of a 1-byte TBD Attribute ID field, a two-byte Length fieldand a TBD attribute body (1630) including the TBD parameter (value)computed by the AP.

As for the TBD attributes, the ΔT attribute is built on the same way,when required. It is defined to have a common general format consistingof a 1-byte AT Attribute ID field, a 2-byte Length field and a ΔTattribute body (1640) including the ΔT value computed by the AP.

The usage of the Information Element inside the MAC frame payload isgiven for illustration only, any other format may be supportable. Thechoice of embedding additional information in the MAC payload isadvantageous in that it keeps legacy compliancy for the medium accessmechanism. This is because any modification performed inside the PHYheader of the 802.11 frame would have inhibited any successful decodingof the MAC header (the Duration field would not have been decoded, sothe NAV would not have been set by legacy devices).

Turning now to other illustrative embodiments of improvements accordingto the invention, one may note that the above-mentioned trigger framemay be dedicated to a specific data traffic, in which case it includes areference to a type of data traffic, for instance any priority or AC asshown in FIG. 3 b.

As a consequence, the management of the RU backoff value may beperformed with respect to a single type of data traffic, i.e. moregenerally with respect to any data regardless of the data traffic. Inother words, the contention for access to the Random RUs according tothese embodiments can be conducted regardless of the ACs.

More generally, these embodiments may apply for transmitting data,regardless of the ACs, meaning that a general transmission buffer isused instead of a plurality of AC queues. In such a case, the referencesbelow to “active AC” are meaningless, and only refer to such generaltransmission buffer.

However, for illustrative purposes, specific implementations taking intoaccount the ACs are described below.

FIG. 13 illustrates an exemplary transmission block of a communicationnode 600 according to illustrative embodiments of the invention.

The node includes:

a plurality of traffic queues 310 for serving data traffic at differentpriorities;

a plurality of queue backoff engines 311, each associated with arespective traffic queue for computing a respective queue backoff valueto be used to contend for access to at least one communication channelin order to transmit data stored in the respective traffic queue. Thisis the EDCA; and

an RU backoff engine 890 separate from the queue backoff engines, forcomputing an RU backoff value to be used to contend for access to theOFDMA resources defined in a received TF (sent by the AP for instance),in order to transmit data stored in either traffic queue in an OFDMA RU.The RU backoff engine 890 belongs to a more general module, namelyRandom RU procedure module 705, which also includes a transmissionmodule, referred to as OFDMA muxer 891.

The conventional AC queue back-off registers 311 drive the medium accessrequest along EDCA protocol, while in parallel, the RU backoff engine890 drives the medium access request onto OFDMA multi-user protocol.

As these two contention schemes coexist, the source node implements amedium access mechanism with collision avoidance based on a computationof backoff values:

-   -   a queue backoff counter value corresponding to a number of        time-slots the node waits, after the communication medium has        been detected to be idle, before accessing the medium. This is        EDCA;    -   an RU backoff counter value (OBO) corresponding to a number of        idle RUs the node detects, after a TxOP has been granted to the        AP over a composite channel formed of RUs, before accessing the        medium. This is OFDMA.

RU backoff engine 890 is in charge of determining appropriate RU backoffparameters based on one or more queue backoff parameters of the queuebackoff engines, in particular during initialization and management ofthe RU backoff value OBO and of its associated congestion window sizenoted CWO. For instance, RU backoff engine 890 computes the RU backoffvalue OBO by randomly selecting a value within a contention (orcongestion) window range [0, CWO], wherein the contention window sizeCWO is selected from selection range [CWO_(min), CWO_(max)].

OFDMA muxer 891 is in charge, when the RU backoff value OBO reacheszero, of selecting data to be sent from one or more AC queues 310 (orthe general transmission buffer in a more general context). Various waysto select the data to be sent from the one or more queues can beimplemented. As it is not the core of the present invention, suchselection approaches are not further detailed here.

One main advantage of embodiments of the present invention is to stillbe able to use, for the OBO/RU backoff engine, a classicalhardware/state-machine of standard back-off mechanism, in particular thebasic mechanism that enables, when a back-off value reaches zero, amedium access to be requested. Adjusting back-off parameters (backoffvalue, contention window min and max) is implemented simply byoverwriting registers.

Upon receiving a Trigger Frame 430, the contention procedure forcounting down the OBO backoff may consist in decreasing the OBO backoffcount value by the number of detected-as-available RUs in the receivedtrigger frame, or in a variant in decreasing the OBO backoff count valueeach elementary time unit (which may be different in size, in particularshorter, compared to the time units used when contending for access tothe 20 MHz communication channels).

The medium access to be requested when OBO is down to zero (or lessthan), may consist in applying a random selection of a RU among thedetected-as-available RUs for sending data (according example of FIG.5). In a variant, the random RUs may be indexed from 1 to Nb_(RU), andthe selected random RU is the one having the RU backoff value OBO(before the above decrementing by the number of detected-as-availableRUs) as index.

According to first improvements of the invention, the Trigger Frame 430includes a correcting “TBD” parameter calculated by the AP, and onerandom resource unit is determined from the detected-as-available randomresource units, based on the received TBD parameter and on one randomparameter local to the node, The random parameter local to the node isfor instance the OBO backoff value randomly selected from contentionwindow range [0, CWO].

According to second improvements of the invention, the contention windowrange [0, CWO] from which any new OBO backoff value is randomly selectedis updated depending on a success or failure in transmitting the dataduring the previous RU access.

Embodiments of the invention are now described with reference to FIGS.14 to 22.

FIG. 14 illustrates, using a flowchart, main steps performed by MAClayer 702 of node 600, when receiving new data to transmit.

At the very beginning, none traffic queue (or the general transmissionbuffer) stores data to transmit. As a consequence, no queue backoffvalue has been computed. It is said that the corresponding queue backoffengine or corresponding AC (Access Category) is inactive. As soon asdata are stored in a traffic queue, a queue backoff value is computed(from corresponding queue backoff parameters), and the associated queuebackoff engine or AC is said to be active.

At step 901, new data is received from an application local running onthe device (from application layer 701 for instance), from anothernetwork interface, or from any other data source. The new data are readyto be send by the node.

At step 902, conventional 802.11 AC backoff computation is performed bythe queue backoff engine corresponding to the type of the received data.

If the AC queue corresponding to the type (Access Category) of thereceived data is empty (i.e. the AC is originally inactive), then thereis a need to compute a queue backoff value for the corresponding backoffcounter.

The node then computes the queue backoff value as being equal to arandom value selected in range [0, CW]+AIFS, where CW is the currentvalue of the contention window size for the Access Category considered(as defined in 802.11 standard and updated for instance in step 1170below), and AIFS is an offset value which depends on the AC of the data(all the AIFS values being defined in the 802.11 standard) and which isdesigned to implement the relative priority of the different accesscategories.

As a result the AC is made active.

Next to step 902, step 903 computes the RU backoff value OBO if needed.

An RU backoff value OBO needs to be computed if the RU backoff engine800 was inactive (for instance because there were no data in the trafficqueues/general transmission buffer until previous step 901) and if newdata to be addressed to the AP have been received. This step 903 is thusa step of initializing OBO.

It first includes initializing the Contention Window size CWO (note thatCW refers to the conventional contention window size for the ACs whileCWO refers to the contention window size for the RU/OBO backoff,specific to embodiments of the invention) as explained below withreference to FIG. 15, and then computing RU backoff value OBO from CWO.

In particular, RU backoff value OBO may be determined as a randominteger selected from contention window range [0, CWO] uniformlydistributed: OBO=random[0, CWO]. This is why the random RUs selected bythe nodes for transmission are based on one random parameter local tothe node.

In variants, RU backoff value OBO may be determined by adding, to avalue randomly selected from contention window range [0, CWO] uniformlydistributed, a value computed from one or more arbitration interframespaces, AIFS:

OBO=random[0, CWO]+AIFS[AC].

For instance, AIFS[AC] is either the lowest AIFS value from the EDCAAIFS value or values of the active AC or ACs in considered node 600, oran average value from the same the EDCA AIFS value or values.

According to the first embodiments of the invention, RU backoff valueOBO is determined based on a correcting parameter TBD, such as an RUcollision and unuse factor, received from the AP (in the Trigger Frame),for instance because CWO itself may be computed from TBD parameter. TheRU collision and unuse factor TBD is further explained below. It is anadjustment parameter transmitted by the AP to drive node 600 to adjustits RU backoff value OBO. This adjustment parameter preferably reflectsthe AP point of view of collisions on RUs and/or of unuse of RUs, in theoverall 802.11ax network.

Thus, the RU collision and unuse factor TBD is preferably function ofthe number of unused random resource units and of the number of collidedrandom resource units in one or more previous trigger frames, asdetected by the AP.

Symmetrically, it may also be function of a number of random resourceunits that are used by the nodes and that do not experience collisionduring the one or more transmission opportunities.

Next to step 903, the process of FIG. 14 ends.

For completeness of description, an exemplary determination of TBDparameter is provided. It takes place at the AP upon providing randomRUs in trigger frames. The number of RUs in the trigger frame may alsoevolve simultaneously.

FIG. 20 illustrates, using a flowchart, general steps of a wirelesscommunication method at the AP adapted to compute the TBD parameter orRU collision and unuse factor TBD. It is a slight adaptation of theprocess of FIG. 11. Such TBD information is encapsulated inside a newTrigger Frame (TF) sent by the AP, for instance as already explainedabove with reference to FIG. 12.

According to some embodiments, the TBD parameter is added to TF only ifit is relevant, i.e. if its use improves efficiency of the network.Implementations of this approach are described below with reference toFIG. 21.

Upon receiving an uplink OFDMA frame (1501), the AP is in charge ofsending an acknowledgment frame to acknowledge safe reception oftransmitted data by all or part of the nodes over the OFDMA RUs (1502).

At step 1503, the AP analyses the number of collided and empty (i.e.unused) OFDMA random RUs. It may perform this step by sensing each RUforming the composite channel. These values are used to update OFDMA usestatistics. In particular, the AP determines statistics on randomresource units not used by the nodes during the transmission opportunityand/or random resource units on which nodes collide during thetransmission opportunity.

The OFDMA use statistics are used by the AP at steps 1504-1505 todetermine various parameters to dynamically adapt (from one TXOP to theother) the contention scheme of the nodes for accessing the Random RUs.

It includes determining the TBD parameter for the next OFDMAtransmission (1504).

It may also include determining and thus modifying the number of randomresource units within the communication channel for the nexttransmission opportunity (1505).

Steps 1504-1508 thus dynamically adapt (from one TXOP to the other) thecontention scheme of the nodes for accessing the Random RUs, by bothadjusting the TBD parameter and the number of Random RUs available forthe nodes.

It may be considered the case where all (or more than 80%) OFDMA RandomRUs are used in the last OFDMA TXOP (or N previous OFMDA TXOPs, N beinginteger). It means that many nodes are requesting to transmit data. As aconsequence, the number of Random RUs for the next OFDMA transmissioncan be increased by the AP (for instance by 1 up to a maximum number),while the TBD parameter can remain the same.

In addition, if collisions occur on several used OFDMA Random RUs (atleast for instance more than a third), it means that the TBD parametershould be decreased to minimize the collisions between the nodes duringthe RU allocation. For instance, the TBD parameter may be decreased byabout 30%.

A drawback of decreasing the TBD parameter (in case it is used as adivisor of the RU backoff value OBO by the nodes) is that the Random RUallocation is less optimized.

On the other hand, if several OFDMA Random RUs remain unused (at leastfor instance more than a third—or less than 50% of the RUs are used),the TBD parameter can be increased, for instance by 30%, and/or thenumber of Random RUs for the next OFDMA transmission can be decreased bythe AP (for instance by 1) to optimize the OFDMA Random RU allocation.

A drawback of increasing the TBD parameter is that the collisions duringthe Random RU allocation may increase.

This illustrates that, upon termination of each uplink OFDMA TXOP, theupdating of the TBD parameter is a trade-off between minimizingcollisions during Random RU allocation and optimizing the filling of theOFDMA Random RUs.

To be precise, at step 1504, the AP may compute a new TBD parameterbased on the determined OFDMA use statistics, optionally further basedon the number of nodes transmitting on the random resource units duringthe previous transmission opportunity. Note that the OFDMA usestatistics may be statistics on the previous TXOP only or on N (integer)previous TXOPs.

In variants, the TBD parameter may be a percentage according to thecollision ratio detected by the AP among the OFDMA RUs, and/or the ratioof unused OFDMA RUs in previous MU OFDMA transmission opportunitiesand/or the ratio of used and non-collided OFDMA RUs. Depending onwhether the TBD parameter is a percentage or an integer value, theformulae involving TBD may be slightly adapted, in particular at thenodes.

For instance, the TBD parameter includes a value used together with arandom parameter local to each node, for the node to determine which oneof the random resource units to access. For instance, the randomparameter can be based on an RU backoff value used by the node tocontend for access to the communication channel, and the TBD parametermay be used to define the contention window size CWO from which the RUbackoff value is randomly selected.

In embodiments where the TBD parameter is used to define the contentionwindow size CWO at the nodes, the TBD parameter may be function of aratio between the number of collided random RUs and the number of randomRUs in the one or more transmission opportunities. The other ratiodefined above may also be used.

The above ratio may be multiplied by a predefined factor, for instance0.08, such that TBD is function of CRF=α.(Nb_collided_RU/Nb_RU_total)with α=0.08.

Using this formula advantageously makes it possible for the AP todetermine an optimum CWO for the nodes without knowledge of the numberof concurrent nodes. Indeed, the AP cannot know the number of nodeshaving tried to send data by analysing the result of transmissions inresponse to a previous trigger frame, because the AP cannotdifferentiate between the different nodes colliding on a single RU (thecollision detection result is the same if 2 or more nodes arecolliding).

However, statistically, the proportion of collided RUs reflects thenumber of concurrent nodes. So if the AP analyses the number of collidedRUs from the previous TFs and creates corresponding statistics, it canuse them to determine CWO.

In details, increasing CWO is a way to adapt the frequency at which thenodes try to access the medium, to the effective number of free channels(number of random RUs). So the AP just needs to determine value CRFaccording to the collided RU statistics, which in turns can be appliedto CWO_(min) value to adapt CWO.

In specific embodiments, TBD equals this value CRF.

In other specific embodiments, TBD equals 2̂CRF (̂ being the powerfunction).

In yet other specific embodiments, TBD directly defines the contentionwindow size to be used by the nodes, i.e. directly defines CWO. Forinstance, TBD=CWO_(min)*2̂CRF, where CWO_(min) is a (predetermined) lowboundary value.

Indeed, CWO is selected from [CWO_(min), CWO_(max)]. CWO_(min) is thelower boundary of a selection range from which the nodes select thecontention window size to use to contend for access to the random RUs.Symmetrically, CWO_(max) is the upper boundary of the selection rangefrom which the nodes select the contention window size to use to contendfor access to the random RUs.

As an example, CWO_(min) is (or more generally may be determined as afunction of) the number of random resource units defined in the triggerframe (in which TBD is to be encapsulated).

Defining TBD as CWO to be used by the nodes advantageously avoids havingthe nodes performing a certain number of tries before reaching anoptimum CWO value. Indeed, the AP has an overall view of the traffic inthe network, and thus can directly compute an optimum CWO for the nodes.Higher stability in latency is thus achieved.

In other specific embodiments, TBD is used to define the above selectionrange. For instance, TBD as provided by the AP defines CWO_(min) ordefines CWO_(max).

Setting CWO_(max) with TBD advantageously makes it possible for the APto control the maximum latency, in particular if the nodes increasetheir CWO as they experience data collisions in the accessed random RUs.Thus the AP globally controls the latency in the network.

This is for example useful in the scenario where the AP wants to gettimely reports from the nodes (by using aging mechanisms, i.e.cancelling outdated packets, to avoid outdated report emission), such asbuffer status or MIMO efficiency reports (sounding reports).

Furthermore, it may be noted that increasing CWO_(max) may enhanceefficiency of random RU usage (i.e. number of used random RUs withoutcollisions). Thus, CWO_(max) set by the AP through the TBD parameter maybe a tradeoff between the maximum latency and RU usage efficiency.

In yet other embodiments, TBD may also be used to identify an entry toselect in a predefined table of contention window sizes.

Such a table may be shared between the AP and the nodes or can bepredetermined at each node. Thus the AP identifies a CWO value to beused by the nodes from the table, by specifying an entry index therein.

These values can be adjusted as the OFDMA use statistics show that toomany collisions occur on the Random RUs or too many Random RUs remainunused.

Any of the TBD parameters above may be adjusted or adapted to a specificgroup of nodes in which case the TBD parameter is preferably computedfrom OFDMA use statistics related to the nodes of the specific group, ifsuch statistics can be identified. This is to assign differentpriorities to different groups of nodes, and to control different QoSbetween the node groups. Preference is given to setting different valuesof CWO through TBD, instead of different values of CWO_(max) forinstance, because it provides a finer granularity/better control of thediscrimination/prioritization between the node groups (by settingCWO_(max) for different node groups, the discrimination is obtained onlywhen CWO in one group is above CWO_(max) of another group).

Different groups of nodes may be identified through different BSSIDs,thus corresponding to different virtual sub-networks managed by the AP.

In a variant to the node group approach or in combination therewith,different TBD parameters (values) may be set for different types of data(ACs). Since the trigger frame may be restricted to a specific type ofdata (specified in the frame), a corresponding TBD parameter may beprovided to drive the nodes along a specific behaviour when accessrandom RUs to transmit this type of data. In this way, the AP can managethe latency of given type of required data.

This optional assignment of the TBD value to a group (BSSID) of nodes orto a type of data is shown through optional blocks 1505 and 1506 in theFigure. Step 1505 checks whether a specific requirement is defined atthe AP, in which case the assignment is performed at step 1506.

Next, at step 1507, the AP determines the number of Random RUs toconsider for the next multi-user TXOP about to be granted (because theAP can pre-empt the wireless medium over the nodes, since it must waitfor the medium to be idle during a shorter duration than the waitingduration applied by the nodes).

The determination of step 1507 can based on the BSS configurationenvironment, that is to say the basic operational width (namely 20 MHz,40 MHz, 80 MHz or 160 MHz composite channels that include the primary 20MHz channel according to the 802.11ac standard).

For the sake of simplicity, one may consider that a fixed number ofOFDMA RUs is allocated per 20 MHz band by the 802.11ax standard: in thatcase, it is sufficient that the Bandwidth signaling is added to the TFframes (i.e. 20, 40, 80 or 160 MHz values is added). Typically, suchinformation is signaled in the SERVICE field of the DATA section ofnon-HT frames according the 802.11 standard. As a consequence,compliance with 802.11 is kept for the medium access mechanism.

Note that in embodiments where the number of random RUs is kept fixed,step 1507 may be avoided.

Next to step 1507, the OFDMA use statistics may also be used to evaluatea use efficiency of the random resource units based on the determineduse statistics. The related steps 1508 to 1511 are implemented when aswitch between the AP-initiated mode and the local mode to drive thecomputation of CWO by the nodes is searched.

Step 1508 evaluates the use efficiency of the random resource unitsbased on the determined OFDMA use statistics. A metric or measure,function of a number of random resource units that are used by the nodesand that do not experience collision during the one or more transmissionopportunities, can be used. It means that the use efficiency metric isbased on statistics on the RUs that have been successfully used by thenodes (i.e. neither the collided random RUs nor the non-used randomRUs).

For instance, the evaluated use efficiency measure may include a ratiobetween the number of random resource units that are used by the nodesand that do not experience collisions, and a total number of randomresource units available during the one or more transmissionopportunities. This metric thus mirrors how efficiently the availablerandom RUs have been used.

In variants, the evaluated use efficiency measure may include a ratiobetween a number of collided random resource units and the total numberof random resource units available during the one or more transmissionopportunities.

In another variant, the evaluated use efficiency measure may include aratio between a number of unused random resource units and the totalnumber of random resource units available during the one or moretransmission opportunities.

Of course, other formulae mixing the above numbers can be used, providedthat they mirror how efficiently the available random RUs have beenused.

All of these alternative metrics are based on use statistics accumulatedduring the one or more transmission opportunities. Any number oftransmission opportunities considered can be envisioned. Also, all thetransmission opportunities within a sliding time window can be takeninto account, as a variant.

Next to step 1508, step 1509 consists in determining whether theevaluated use efficiency measure (e.g. any ratio defined above)indicates that the random RUs are efficiently used or not.

Indeed, FIG. 13 shows that sometimes the local mode is more efficientthan the AP-initiated mode, and sometimes the reverse happens. Takinginto account this information, it is worth trying to switch to the othermode in case the current use efficiency measure is too low.

Thus depending on the evaluated RU efficiency measure, the TBD parametersent to the nodes to drive them in computing their own RU contentionwindow size CWO should be set to a dedicated value or an UNDEFINEDvalue.

Thus the access point decides, based on the evaluated use efficiencymeasure, between the two modes, from which results the decision totransmit or not, to the nodes, the determined TBD parameter within thenext trigger frame to drive the nodes in determining their owncontention window size.

A simple approach may be used, for instance by comparing the evaluateduse efficiency measure to an efficiency threshold, e.g. 30%, todetermine whether the current use of the random RUs is efficient or not.

For instance, if the evaluated use efficiency measure is below theefficiency threshold, a TBD Information Element (to be included in thenext trigger frame as described above with reference to FIG. 12) is setto the TBD parameter as determined at step 1504. This is step 1511. Thisaims at transmitting, to the nodes, the determined TBD parameter TBDwithin a next trigger frame for reserving a next transmissionopportunity, in case of low use efficiency.

On the contrary, in case of an evaluated use efficiency measure abovethe efficiency threshold, a local approach for computing CWO issufficient. In this case, the TBD Information Element is set to anUNDEFINED (or UNUSED) value. This is step 1510 for the AP to have a nexttrigger frame to transmit that does not define a TBD parameter to drivenodes in defining their own contention window size. In this particularcase, the transmitted next trigger frame includes a TBD parameter fieldset to undefined.

Of course, more complex use efficiency metrics (more complex to theratios mentioned above) and more complex tests for step 1509 can be usedto evaluate whether it is opportune to switch to one or the other modebetween the local and AP-initiated modes.

A variant is shown in FIG. 20a based on an hysteresis cycle.

To switch from one of the local or AP-initiated mode to the other, twopredefined efficiency thresholds (THR1 and THR2) may be defined in orderto avoid noisy switching. The two thresholds are used in an hysteresiscycle, to lock a current mode as long as an unlocking criterion (e.g. acomparison with THR2) is not reached. With this hysteresis cycle, theaccess point decides to switch from a current mode among a first mode inwhich the determined TBD parameter is transmitted within a trigger frameand a second mode in which the determined TBD parameter is nottransmitted, to the other mode when the evaluated use efficiency measurefalls below a first predefined efficiency threshold.

The evaluated use efficiency measure is first compared to THR1, forinstance 30% in case the measure used includes a ratio between thenumber of random resource units that are used by the nodes and that donot experience collisions, and a total number of random resource unitsavailable during the one or more transmission opportunities. This isstep 1550.

In case the evaluated use efficiency measure is less than THR1 (output“yes”), it is determined at step 1551 whether the current mode (eitherlocal or AP-initiated) is locked or not. The lock may be implementedusing one bit in a memory or register.

If it is locked (output “yes” at test 1551), no switch can be performedand the current mode is kept. The next step is step 1555.

Otherwise (output “no” at test 1551), the current mode can be switchedto the other mode, i.e. either local mode to AP-initiated mode, or thereverse. This is step 1552, at the end of which the new mode is locked(a locking bit in the register is set to “on”). The next step is step1555.

Back to step 1550, if the evaluated use efficiency measure is above THR1(output “no” at test 1550), the next steps are used to determine whetheror not the current mode can be unlocked.

To do so an unlocking criterion is evaluated at step 1553 using THR2,for instance the evaluated use efficiency measure is compared to THR2,e.g. 32% for the above mentioned ratio. This idea behind step 1553 is toallow the current mode to be unlocked only if it has provided somebenefits in the use of the random RUs.

If the unlocking criterion is not met (e.g. the evaluated use efficiencymeasure remains below THR2), the current mode is kept locked by going tonext step 1555.

Otherwise (the unlocking criterion is met), the current mode is unlocked(the locking bit in the register is set to “off”). It means that thecurrent mode is locked until an evaluated use efficiency measure reachesa second predefined efficiency threshold. The next step is step 1555.

In a variant shown through the optional step 1556, it may be decided tounlock the current mode in case the last mode switch occurred a longtime ago (a time threshold may be used). This is to avoid blocking thenetwork in a specific mode with low efficiency, in case the other modecould provide better results. Indeed, after the unlocking due to expiryof the time threshold, the AP can switch to the other mode in case theevaluated use efficiency measure remains low.

Following the hysteresis steps, step 1555 consists to set the TBDInformation Element to the appropriate value depending on the currentmode. If the current mode is the local mode, then the TBD InformationElement is set to UNDEFINED (similarly to step 1510). On the other hand,if the current mode is the AP-initiated mode, the TBD InformationElement is set to the TBD parameter (value) obtained at step 1504(similarly to step 1511).

Once the TBD Information Element has been set at step 1510 or 1511 (or1555 in FIG. 20a ), it is inserted in the next trigger frame to be sent.Thus, next steps 1512/1513 consist for the AP to build and send the nexttrigger frame with the above determined information: Random RUsinformation and TBD value (in the TBD Information Element).

It is expected that every nearby node (legacy or 802.11ac, i.e. which isneither STA1 nor STA2) can receive the TF on its primary channel. Eachof these nodes then sets its NAV to the value specified in the TF frame:the medium is thus reserved by the AP.

The process of FIG. 20 can be performed at each new trigger frame (step1501 occurs following transmissions triggered by a trigger frame).However, it may be contemplated performing the process at each N(integer) trigger frames, in order to reduce the maximum frequency ofswitching. This is to have time to accurately evaluate the RU useefficiency of the mode (local or AP-initiated) to which the network hasswitched.

FIG. 15 illustrates, using a flowchart, main steps for setting(including initializing) CWO at node 600. In other words, it describes afirst sub-step within step 903 to prepare a random access (contention)for (UL) MU OFDMA transmission in the context of 802.11. It may includecomputing RU backoff parameters.

It starts initially when node 600 receives (e.g. locally from upperlayer 701) new data in any of its AC queue 310 or its generaltransmission buffer, to be addressed to the AP.

At step 1000, node 600 determines the number Nb_(RU) of random RUs, i.e.of the RUs available for contention, to be considered for the multi-userTxOP upon next grant. This information may be provided by the AP throughbeacon frames or trigger frames themselves, or both. For instance, theinformation may be retrieved from the last TF detected. An initial valuemay be used as long as no TF (or beacon frame) is detected.

When the information is conveyed inside a Trigger Frame TF, it may bededuced by counting the number of random RUs, that is to say each RUhaving an associated address identifier (AID) equal to 0 (contrary toScheduled RUs which have non-zero AIDs).

Step 1000 may be optional in embodiments where the RU backoff parameters(and thus the computation of CWO) are not function of the number Nb_(RU)of random RUs.

Next, at step 1001, node 600 obtains queue backoff parameters for theactive ACs. Indeed, they may be used to compute the RU backoffparameters for OFDMA access as described below. These queue backoffparameters may be retrieved from the active queue backoff engines 311.At step 903, we know that at least one AC is active, but also that datait stores are intended to the AP.

Each active AC maintains contention window size CW of its contentionwindow range [0,CW] within the interval [CW_(min), CW_(max)], and usesit to select the random queue backoff value.

Thus, examples of queue backoff (AC) parameters are the following:

-   -   boundaries (CW_(min), CW_(max));    -   arbitration interframe spaces (AIFS);    -   contention window size CW.

Next to step 1001, step 1002 consists for node 600 in computing theselection interval [CWO_(min), CWO_(max)] and then CWO. It may be basedon the retrieved queue backoff parameters.

In the first improvements of the invention, step 1002 is based on theTBD parameter received from the AP in a Trigger Frame, in particular thelast received Trigger Frame. In particular, the contention window size,i.e. CWO, is determined (directly or indirectly through CWO_(min) and/orCWO_(max)) based on the TBD parameter received from the access point.

In the second improvements of the invention, step 1002 is based on asuccess or failure in transmitting data during a previous RU access. Alocal value of CWO may be doubled or the like in case of failure, inorder to restrict transmissions in case of collisions, which in turnreduces the probability of collisions and thus improves use of thecommunication network.

Step 1002 may include two sub-steps:

-   -   a first sub-step to determine CWO_(min) and CWO_(max), wherein        at least one of CWO_(min) and CWO_(max), preferably both, is an        RU backoff parameter determined based on one or more queue        backoff parameters;    -   a second sub-step to compute or select CWO from range        [CWO_(min), CWO_(max)].

This ensures CWO to be dependent on the current EDCA parameters, such asthe CWs. As a consequence, this advantageously takes into account thepriorities raised by EDCA ACs in the process of computing the RU backoffparameters for OBO.

However, in a more general approach that does not take into account thedata traffic ACs, CWO_(min) and CWO_(max) can be computed using otherparameters or using the backoff parameters defining the sole generaltransmission buffer.

According to some embodiments of the second improvements, CWO_(min) andCWO_(max) and CWO are computed only from information computed locally bynode 600. This is for instance the case in the process of FIG. 18described below.

Regarding the first sub-step, as the targeted transmission is of ULOFDMA type, RU backoff parameters CWO_(min) and CWO_(max) should becomputed differently than the corresponding CW_(min)/CW_(max) values ofthe EDCA scheme.

As an example, CWO_(min) may be set to the number of random resourceunits defined in a received trigger frame: CWO_(min)=Nb_(RU). Thisimproves usage OFDMA RUs. This advantageously does not take into accountthe ACs.

As another example, CWO_(min) may be the lowest lower boundaries(CW_(min)) from selection intervals [CW_(min),CW_(max]) of the activequeue backoff engines at node 600, i.e. having non-zero queue backoffvalues:

CWO_(min)=Min({CW_(min)}_(active AC)). This option is preferablyperformed when the CW_(min) are greater than the number of random RUs.Indeed, there is no interest to have CW_(min) lower than Nb_(RU) sincethe risk of collisions would be very high.

As another example, CWO_(min) may be set both according to the lowestlower boundaries (CW_(min)) from selection intervals [CW_(min),CW_(max)]of the active queue backoff engines at node 600 (i.e. having non-zeroqueue backoff values), and according to the number of random RUs:

CWO_(min)=Min({CW_(min)}_(active AC))×Nb _(RU).

In case of a single general transmission buffer, CW_(min) for thisbuffer may be used to compute CWO_(min) according any of the aboveformulae.

Similarly regarding CWO_(max), it may be set to an upper boundary(CW_(max)) of a selection interval [CW_(min),CW_(max)] of the activequeue backoff engine 311 having the lowest non-zero queue backoff value,i.e. the next AC to transmit, reflecting the highest priority AC:CWO_(max)=(CW_(max))_(lowest non-zero AC). This exemplary configurationadvantageously takes the same priority as the AC.

In another example, CWO_(max) may be a mean of upper boundaries(CW_(max)) of selection intervals [CW_(min),CW_(max)] of the activequeue backoff engines 311, i.e. having non-zero queue backoff values:

CWO_(max)=average({CW_(max)}_(active AC)). This exemplary configurationadvantageously takes a medium priority, and is more relaxed compared tothe first exemplary configuration.

In another example CWO_(max) may be the highest upper boundaries(CW_(max)) from selection intervals [CW_(min),CW_(max)] of the activequeue backoff engines 311, i.e. having non-zero queue backoff values:

CWO_(max)=max({CW_(max)}_(active AC)). Thus node 600 is even morerelaxed. This exemplary configuration advantageously ensures that OFDMAwill not take a medium priority lowest than EDCA.

In case of a single general transmission buffer, CW_(max) for thisbuffer may be used to compute CWO_(max) according to any of the aboveformulae.

According to a particular option, the various configurations may be usedin turns, instead of selecting only one of them. Either theconfiguration to use is randomly selected, or it may be based on usestatistics: for instance if feedback information of large number ofcollisions is received, the third configuration may be used. Anotherconfiguration will be used as soon as the feedback information informsof a number of collisions under a predefined threshold.

Regarding the second sub-step, CWO may be initially assigned theCWO_(min) value. Exemplary embodiments for updating of CWO are describedbelow with reference to FIG. 17. CWO may be allowed to increase up tothe upper bound CWO_(max) value as the node attempts to access and userandom RUs.

For instance, CWO is updated depending on a success or failure intransmitting the data when accessing one or more random RUs.

In embodiments, CWO is doubled in case of transmission failure, and maystart with an initial value equal to CWO_(min). As successive attemptsfail, CWO=CWO_(min)*2^(n), where n is the number of successivetransmission failures for the node computing CWO.

In other embodiments that takes into account variations over time,CWO(t)=CWO_(min)(t)*2^(n), where n is the number of successivetransmission failures. Specifically, CWO_(min)(t) may be the number ofrandom resource units defined in a current trigger frame received attime t, i.e. the last received trigger frame.

According to some embodiments of the first improvements, at least one ofCWO_(min) and CWO_(max) and CWO depends on the RU collision and unusefactor TBD received from another node (preferably from the AccessPoint). This is for instance the case in the process of FIG. 19described below. As CWO usually depends on CWO_(min) and CWO_(max) (itis selected from the selection range defined by these two values), thecontention window size CWO is also determined based on the TBD parameterreceived from the access point when it is CWO_(min) or CWO_(max) thatdirectly depends on TBD.

For instance, CWO_(min) may be computed as described above for thesecond embodiments of the invention (e.g. CWO_(min) is the number ofrandom resource units defined in the trigger frame), and CWO may befunction of CWO_(min) and of the received TBD parameter. As an example,CWO is set to 2^(TBD)*CWO_(min). Note that this value may be upperbounded by a CWO_(max) value as determined above.

As a variant, CWO is set to TBD*CWO_(min).

Of course, these variants mirror the variants implemented at the AP tocompute TBD. The transmitted TBD parameter is such that the finalcalculation of CWO is preferably according to the following formula:2^(CRF)*CWO_(min), wherein CRF=α*(Nb_collided_RU/Nb_RU_total).

In other embodiments, CWO is directly TBD as received.

In yet other embodiments, CWO_(min) or CWO_(max) is directly TBD asreceived. Then CWO may be randomly selected from [CWO_(min), CWO_(max)]and indirectly depends on the TBD parameter received from the AP.

In yet other embodiments, CWO is selected as an entry of a predefinedtable of contention window sizes (defined above with reference to FIG.20), wherein TBD received from the access point identifies the entry toselect in the predefined table.

However, as long as the TBD parameter is not received, optional variantsmay be implemented. In a first variant, the second embodiments of theinvention as defined above may be applied meaning that an initial value(CW_(min)) is assigned to CWO. In a variant, a local RU collision factorCF, thus built locally for instance from past history, may be used. Thisability for the node to switch between a global (AP-initiated) approachand a node local approach is further explained below, in particular withreference to FIG. 21.

Next to step 1002, step 1003 checks whether a triggering event forupdating the RU backoff parameters is detected, before a new OFDMAaccess is performed.

Some triggering events may come from the AP.

For instance, similarly to the EDCF parameters (AIFS[AC], CW_(min)[AC]and CW_(max)[AC]), the AP may announce the number Nb_(RU) of random RUsthrough beacon frames, of alternatively (or in combination with) throughthe trigger frames. Indeed, the AP can dynamically adapt the numberNb_(RU) of RUs depending on network conditions. An example of suchadaptation is given above in connection with the building of the TBDparameter at AP side. Thus a triggering event for node 600 may bereceiving a new trigger/beacon frame defining a number of randomresource units that is different from a current known number of randomresource units.

Other triggering events may be produced locally by node 600.

For instance, as mentioned above, data newly stored in a previouslyempty AC traffic queue 310 activate the corresponding queue backoffengine 311. A corresponding triggering event may thus be detecting thatan empty traffic queue from the plurality of traffic queues has nowreceived data to transmit, in which case the CW parameters of this newlyactivated queue backoff engine may be taken into account to compute theCWO range anew.

More generally, a triggering event may consist in detecting a change inat least one queue backoff parameter used to determine the one or moreRU backoff parameters, i.e. when one of the reference queue backoffparameters has changed. Note that it is not the case for beacon framesindicating the same parameters.

In specific embodiments, illustrated for instance in the process ofFIGS. 17 and 18, a triggering event may be the end of OFDMA transmissionand thus the reception of a positive or negative acknowledgment of aprevious transmission of data in an RU.

In other specific embodiments, illustrated for instance in the processof FIG. 19, a triggering event may be the reception of a new triggerframe.

Upon receiving any triggering event, the process of FIG. 15 loops backto step 1000 to obtain Nb_(RU) and queue backoff parameters again ifappropriate and then to compute new RU backoff parameters.

This ends the process of FIG. 15.

FIG. 16 illustrates, using a flowchart, steps of accessing the mediumbased on the conventional EDCA medium access scheme.

Steps 1100 to 1120 describe a conventional waiting introduced in theEDCA mechanism to reduce the collision on a shared wireless medium. Instep 1100, node 600 senses the medium waiting for it to become available(i.e. detected energy is below a given threshold on the primarychannel).

When the medium becomes free, step 1110 is executed in which node 600decrements all the active (non-zero) AC[] queue backoff counters 311 byone.

Next, at step 1120, node 600 determines if at least one of the ACbackoff counters reached zero.

If no AC queue backoff reaches zero, node 600 waits for a given timecorresponding to a backoff slot (typically 9ps), and then loops back tostep 1100 in order to sense the medium again.

If at least one AC queue backoff reaches zero, step 1130 is executed inwhich node 600 (more precisely virtual collision handler 312) selectsthe active AC queue having a zero queue backoff counter and having thehighest priority.

At step 1140, the data from this selected AC are selected fortransmission.

Next, at step 1150, node 600 initiates an EDCA transmission, in case forinstance an RTS/CTS exchange has been successfully performed to have aTxOP granted. Node 600 thus sends the selected data on the medium,during the granted TxOP.

Next, at step 1160, node 600 determines if the transmission has ended,in which case step 1170 is executed.

At step 1170, node 600 updates CW of the selected traffic queue, basedon the status of transmission (positive or negative ack, or no ackreceived). Typically, node 600 doubles the value of CW if thetransmission failed until CW reaches a maximum value defined by thestandard 802.11 and which depends on the AC type of the data. If thetransmission is successful, CW is set to a minimum value also defined bythe 802.11 standard and which is also dependent on the AC type of thedata.

Then, if the selected traffic queue is not empty after the EDCA datatransmission, a new associated queue backoff counter is randomlyselected from [0,CW], like in step 902.

This ends the process of FIG. 16. Note that this process can be appliedin a similar manner (but with only one AC queue) in case a singlegeneral transmission buffer is considered.

FIG. 17 illustrates, using a flowchart, exemplary steps for updating theRU backoff parameters and value upon receiving a positive or negativeacknowledgment of a multi-user OFDMA transmission.

It is recalled that in a simple implementation, the RU backoff value OBOis used to determine if node 600 is eligible to contend for access to anOFDMA resource unit: OBO should be not greater than the number ofavailable random RUs in order to allow for an UL OFDMA transmission fornode 600. Scheduled RUs are accessible to node 600 if indicated as suchby the AP, independently of RU backoff value OBO.

Thus step 1200 happens during such an UL OFDMA transmission in a randomRU (when decremented OBO reaches zero).

Step 1201 is executed when the UL OFDMA transmission finishes on anaccessed random RU, upon having the status of transmission; either byreceiving a positive or negative acknowledgment from the AP, or byinferring loss of data (in case no ack is received).

At step 1201, the contention window size CWO is updated depending on asuccess or failure in transmitting the data. This step and followingstep 1202 are performed if needed only. In particular, if the endingtransmission has sent all the data intended to the AP (i.e. no more ofsuch data remain in all the traffic queues), there is no need to keepthe RU backoff engine active. It is thus deactivated, by clearing OBOvalue.

If the update is needed, when an OFDMA transmission fails (e.g. thetransmitted data frame has not been acknowledged), a new CWO value maybe computed for instance.

In particular, CWO may be doubled, for instance CWO=2×(CWO+1)−1 orCWO=2*CWO. This illustrates some embodiments of the second improvements.

As CWO may be initially assigned CWO₀=CWO_(min) value and may increaseup to CWO_(max) value, this approach makes that CWO_(n)=CWO₀*2^(n),where n is the number of successive fails when trying to access thenetwork and send data. For instance CWO₀=CWO_(min) as defined above.More precisely, CWO_(n)=min (CWO₀*2^(n); CWO_(max)).

To illustrate this, three successive attempts may be considered asfollows:

For the first access attempt: CWO=CWO₀

For the second access attempt: CWO=CWO₁=CWO₀*2¹

For the third access attempt: CWO=CWO₂=CWO₀*2²=CWO₁*2.

In other embodiments of the second improvements,

CWO_(n)=min (CWO_(min)(t)*2^(n); CWO_(max)).

Again, n is the number of successive failing attempts. CWO_(min)(_(t))is a value that evolves over time. Indeed, [CWO_(min), CWO_(max)] fromwhich CWO is selected may evolve over time.

For instance, as the number of random RUs in the trigger frames usuallyevolves over time, it may be worth updating CWO_(min) based on thisevolving number of random RUs. This is why CWO_(min) evolves over time,as noted by CWO_(min)(t).

Thus the above embodiments take into account the TF characteristicschanges (number of random RUs) as well as the collision history (failingattempts). This may be important in network that substantially evolvesover time. Indeed, the probability to have two successive trigger frameswith the same characteristics (same number of random RUs, same type ofdata required, same width of the RU, etc.) may be low. So an approachable to dynamically adapt the CWO value to the current TFcharacteristics provides benefits.

To illustrate this dynamic approach, let consider three successiveattempts, as follows:

For the first access attempt: CWO=CWO_(min) (t=0)=Nbr_rRU (number ofrandom RUs) of TF0, where TF0 is the trigger frame corresponding to thefirst transmission attempt by node;

For the second access attempt (in case of failing first attempt):CWO=CWO₁=CWO_(min)(t=1)×2¹, where CWO_(min) (t=1)=Nbr_rRU of TF1, whereTF1 is the trigger frame corresponding to the second transmissionattempt by node. Nbr_rRU of TF1 can be different from Nbr_rRU of TF0;

For the third access attempt: CWO=CWO₂=CWO_(min)(t=2)×2²,

where CWO_(min) (t=2)=Nbr_rRU of TF2, where TF2 is the trigger framecorresponding to the third transmission attempt of current data bystation

In variants illustrating some embodiments of the first improvements, anew CWO value may be obtained using TBD as received from the AP asdescribed above, e.g. CWO=2^(TBD)*CWO_(min) or CWO=TBD*CWO_(min) orCWO=TBD or CWO is defined by the table entry having TBD as entry index,or CWO is randomly selected from [CWO_(min), CWO_(max)] where CWO_(min)or CWO_(max) equals TBD, depending on which approach the AP adopts.

This reduces the collision probability in case there are too many nodesattempting to access the RUs.

In case the OFDMA transmission succeeds, CWO may be reset to a(predetermined) low boundary, such as CWO_(min).

This description of step 1201 reflects a local point of view at node600.

Next to step 1201, step 1202 consists in computing a new RU backoffvalue OBO based on the updated contention window size CWO. The sameapproaches as described above with reference to step 903 can be used:for instance OBO=random[0, CWO], OBO=random[0, CWO]+AIFS[AC].

This ends the process of FIG. 17.

FIG. 18 illustrates, using a flowchart, first exemplary embodiments ofaccessing the medium based on the OFDMA medium access scheme, and oflocally updating the RU backoff parameters, such as the contentionwindow size CWO, when a new trigger frame is received at transmittingnode 600. This Figure illustrates some embodiments of the secondimprovements according to the invention.

It means that node 600 has data to transmit, and thus has at least oneactive EDCA queue backoff engine 311. Furthermore, node 600 has anon-zero RU backoff value OBO, meaning that it has data to send to theAP upon receiving the trigger frame. The same process can be applied incase the node has a single general transmission buffer, in which case asingle AC queue is considered.

At step 1300, node 600 checks whether or not it has received an 802.11aframe in a non-HT format. Preferably, the type of the frame indicates atrigger frame (TF), and the Receiver Address (RA) of the TF is abroadcast or group address (i.e. not a unicast address correspondingspecifically to node 600′s MAC address).

Upon receiving the trigger frame, the channel width occupied by the TFcontrol frame is signaled in the SERVICE field of the 802.11 data frame(the DATA field is composed of SERVICE, PSDU, tail, and pad parts). Anindication that the control frame is a Trigger Frame may be provided inframe control field 301, which indicates the type of the frame. Inaddition, frame control field 301 may include a sub-type field foridentifying the type of the trigger frame, such as a TF-R.

As noted above, even without such sub-type field, the random RUs can bedetermined using for instance the AID associated with each RU defined inthe TF (AID=0 may mean random RU). So the number of random ResourceUnits supporting the random OFDMA contention scheme is known at thisstage. Obtaining the number of random RUs may be advantageouslyperformed if the number of random RUs varies from one TF to the other.

Next, at step 1301, node 600 consists in decrementing the RU backoffvalue OBO based on the number Nb_(RU) of random resource units definedin the received trigger frame: OBO=OBO−Nb_(RU). This is because node 600is determined as being an eligible node to transmit data in an OFDMArandom RU, if its pending RU backoff value OBO is not greater than thenumber of OFDMA random RUs.

Step 1301 thus updates OBO value upon receiving a new trigger frame.

In a slight alternative, decrementing the RU backoff value is also basedon the RU collision and unuse factor TBD received from another node.

For instance, OBO=(OBO−Nb_(RU))*TBD. As a result, this alternativeembodiment updates RU backoff value OBO with an AP's parameter upon eachOFDMA transmission.

In another example, OBO=OBO−(Nb_(RU)*TBD). This formula thus adapts thespeed of decrementing OBO to the network conditions, through factor TBD.

Next to step 1301, step 1302 consists for node 600 in determiningwhether it is an eligible node for transmission. This means either ascheduled RU of the TF is assigned to node 600 or its RU backoff valueOBO is less or equal to zero.

As alternative, and if node 600 supports concurrent OFDMA transmissioncapabilities, both cases (scheduled RU and OBO is less or equal to zero)are handled and steps 1303 to 1310 are conducted in parallel for the twoaccesses.

In case of no eligibility, the process ends.

In case of eligibility, node 600 selects one RU for sending the data. Itis either the assigned scheduled RU, or a random RU selected from theNb_(RU) random RUs of the TF (either randomly or using the RU backoffvalue OBO before step 1301 as an index to select the random RU havingthe same index). This is step 1303.

Once the RU for OFDMA transmission has been determined, step 1304selects data to transmit to the AP, usually from one or more of theactive AC traffic queues 310. OFDMA muxer 801 is in charge of selectingsuch data to be transmitted, from among at least one AC traffic queue310.

Note that during an MU OFDMA TXOP (i.e. transmission in an RU), node 600is allowed to transmit multiple data frames (MPDUs) from the same ACtraffic queue, with the condition that the whole OFDMA transmissionlasts the duration originally specified by the received trigger frame(i.e. the TxOP length).

Of course, if not enough data is stored in the selected AC trafficqueue, another or more active AC traffic queue may be considered.

Generally speaking, the data frames from the active ACs having thehighest priority are selected. “Highest priority” may means having thelower queue backoff value, or having the highest priority according toEDCA traffic class prioritization (see FIG. 3b ).

Next to step 1304, step 1305 consists for node 600 in initiating andperforming a MU UL OFDMA transmission of the selected data (at step1304) in the selected RU (at step 1303).

As commonly known, the destination node (i.e. the AP) will send anacknowledgment related to each received MPDU from multiple users insidethe OFDMA TXOP (see step 1502).

Preferably, the ACK frame is transmitted in a non-HT duplicate format ineach 20 MHz channel covered by the initial TF's reservation. Thisacknowledgment can be used by the multiple source nodes 600 to determineif the destination (AP) has well received the OFDMA MPDUs. This isbecause source nodes 600 are not able to detect collisions inside theirselected RUs.

Thus at step 1306, node 600 obtains a status of transmission, forinstance receives an acknowledgment frame.

In case a scheduled RU of the TF is assigned to node 600, as the OFDMAaccess is not granted through OBO, then the algorithm goes directly tostep 1309 (arrow not shown in the figure).

Otherwise, the algorithm continues either at step 1307 or at step 1308.In case of positive acknowledgment, the MU UL OFDMA transmission isconsidered as a success and step 1307 is executed. Otherwise, step 1308is executed.

In case of successful OFDMA transmission on the selected random RU, CWOis set to a (predetermined) low boundary value, for instance CWO_(min),at step 1307.

In case of failing OFDMA transmission, CWO is doubled, for instanceCWO=2×(CWO+1)−1, at step 1308. Note that CWO cannot be above CWO_(max).

As mentioned above, other variants exist, for instance: CWO=CWO*2;CWO=CWO_(min)*2^(n); CWO(t)=CWO_(min)(t)*2^(n); etc.

Next to step 1307 or 1308, step 1309 consists for node 600 indeactivating the AC queue backoff engines that have no more data totransmit. This is because due to the UL MU transmission, some AC queuesmay have been emptied from the transmitted data. In such a case thecorresponding queue backoff value is cleared (the value is no longertaken into account to compute the RU backoff values and to EDCA accessthe medium).

As long as the selected (at step 1304) AC queue engines still storesdata to be transmitted in their respective traffic queues, theirrespective (non-zero) queue backoff is kept unchanged. Note that in anycase, as only an OFDMA access has been performed (and not over the EDCAchannel), the AC contention window values CW of the queue backoffengine(s) 311 (EDCA CW) are not modified.

Next to step 1309, step 1310 consists for node 600 to determine whetheror not a new RU backoff value OBO has to be computed. This is becausevalue OBO has expired (test 1302) and data intended to the AP have beenconsumed.

Thus, it is first determined whether or not data intended to the APremain in any of the AC traffic queues. In case of positivedetermination, a new OBO value is computed. Otherwise, the RU backoffengine is deactivated.

The computation of OBO value may be according to any approach describedabove with reference to step 903, for instance OBO is determined as arandom integer selected from contention window range [0, CWO] uniformlydistributed.

This ends the process of FIG. 18.

FIG. 19 illustrates, using a flowchart, second exemplary embodiments ofaccessing the medium based on the OFDMA medium access scheme, and ofupdating the RU backoff parameters, either locally or based on areceived TBD parameter, when a new trigger frame is received attransmitting node 600.

This Figure illustrates some embodiments of the first improvementsaccording to the invention which are based on the TBD parametertransmitted by the AP.

It also illustrates some of the second embodiments, when no TBDparameter is received from the AP. Thus it is also a first illustrationof a decision by the node to switch between these two approaches: theAP-initiated mode to compute CWO (using transmitted TBD) and the localmode (using only values local to the node).

Compared to the example of FIG. 18, the embodiment of FIG. 19 involvesuse of an adjustment/correcting parameter issued from the AP, namely theabove-mentioned TBD parameter, to compute CWO. The TBD parameter,reflecting the AP point of view of collisions in overall 802.11axnetwork, may evolve over time and be provided in the TFs.

Until a first TBD parameter is received by node 600, the latter managesa corresponding local parameter, namely local RU collision factor CF.Local factor CF will allow to use local statistics instead of APparameter for applying steps 1404 to 1405 further explained below.

In this second exemplary embodiment, the computation of RU backoffparameters (including CWO) is performed upon reception of the triggerframe, and not when new data arrive from an upper layer application 701(as in the case of above step 903).

Thus steps 1400 to 1408 are new compared to FIG. 18. Steps 13xx aresimilar to step 13xx of FIG. 18.

After step 1300 of receiving a new TF, step 1400 aims at determiningwhether or not the RU backoff parameters should be initialized uponreceiving the trigger frame. More precisely, step 1400 consists indetermining whether the RU backoff engine is inactive (e.g. OBO value isless or equal to 0) and data intended to the AP are now stored intraffic queues 310 (i.e. it is the first TF received after some firstdata for the AP have been input in the traffic queues).

In step 1400, the node thus determines whether or not the receivedtrigger frame includes a TBD parameter to drive the node in defining itsown contention window size.

In case the RU backoff engine requires to be activated, steps 1401 to1406 are performed to initialize the RU backoff engine, after which step1301 is executed. In case the RU backoff engine is already active, step1301 is directly executed.

The initialization sequence (steps 1401-1406) consists first for node600 in checking whether or not a TBD parameter has been received fromthe AP (step 1401). By sending or not the TBD parameter (i.e. setting aTBD value or an UNDEFINED value in the appropriate field of the triggerframe), the AP thus controls how the nodes compute their own CWO value.

If such TBD parameter has been received, steps 1404-1406 are performed.Otherwise, the un-initialized TBD parameter is initialized with thelocal CF value (step 1403): here node 600 acts alone for adapting theCWO value, that is to say only in regards to the success of its own pastOFDMA transmissions.

The evolving of factor CF is described below with reference to steps1407-1408.

Next to step 1403, step 1404 is performed during which new RU backoffparameters are determined. For instance a new CWO_(min) value isdetermined, using any approach as described above with reference to step1002.

For instance, CWO_(min) may be set with regards to the lowest CW_(min)of the active AC queues: CWO_(min)=Min({CW_(min)}_(active AC)).

In a variant, CWO_(min) may be set with regards to the lowest CW_(min)of the active AC queues and the number of random RUs:CWO_(min)=Min({CW_(min)}_(active AC))×Nb_(RU).

In another variant, CWO_(min) may be set to the number of random RUs asdeclared in the trigger frame received.

In another variant, CWO_(min) may be set to the TBD parameter (which isthus as received from the AP or as set through CF).

Next, step 1405 consists for node 600 in computing CWO. This may be donefrom CWO_(min), and possibly from the TBD parameter.

An example of computation is: CWO=2^(TBD)*CWO_(min) or CWO=TBD*CWO_(min)or CWO=TBD or CWO is defined by the table entry having TBD as entryindex, or CWO is randomly selected from [CWO_(min), CWO_(max)] whereCWO_(min) or CWO_(max) equals TBD. Of course, the formula used maycorrespond to the mere nature of the TBD value sent by the access point,in order for CWO to be preferably equal to CWO=2^(CRF)*CWO_(min),wherein CRF=α*(Nb_collided_RU/Nb_RU_total) as defined above.

CWO value may be limited to an upper bound, for instance CWO_(max)defined above (step 1002).

As a result, if the TBD parameter is 0, then the minimum value of EDCACW_(min) may drive the medium access in caseCWO=2^(TBD)*CWO_(min):CW_(min)=3 for VOICE, so approximately a maximumof two trigger frames to backoff, the third one being the one to accessin the worst case.

Thus in step 1405, the node computes a new contention window size CWObased on the received TBD parameter, in case it is positively determinedthat the received trigger frame includes such TBD parameter, to contendfor access to the random resource units splitting the transmissionopportunity (i.e. to compute a new OBO value—see step 1406 below).Otherwise, the node uses a local contention window size (e.g. derivingfrom local factor CF) as new contention window size, to contend foraccess to the random resource units splitting the transmissionopportunity.

Next, at step 1406, node 600 computes the RU backoff value OBO from CWO.See for instance above step 903: e.g. OBO=random[0, CWO].

Back to the positive output of test 1400, the algorithm of FIG. 18 isreused, except for steps 1307 and 1308. They are replaced by steps 1407and 1408 during which the local RU collision factor CF is updateddepending on a success or failure in transmitting the data (instead ofdirectly updating CWO).

Of course, using the doubling approach of steps 1307 and 1308 forsetting a new CWO is also possible, in which case step 1403 may set TBDto a value corresponding to the new CWO. For instance,TBD=log₂(CWO/CWO_(min)) for the formula CWO=2^(TBD)*CWO_(min).

Factor CF may evolve within the range [0, CF_(max)] if formulaCWO=2^(TBD)*CWO_(min) is used, wherein CF_(max) is a maximumcoefficient: for instance 5. As an alternative, CF_(max) can be drawnaccording the active EDCA AC queues:CF_(max)=[(CW_(max))_(AC)+1]/[(CW_(min))_(AC′)+1],

wherein “AC” and “AC′” designate the active queue backoff engines havingthe highest priority (e.g. the highest EDCA traffic class prioritizationof FIG. 3b ), or having the highest CW_(max) value and lowest CW_(min)value respectively (that is to say CW_(max)=1023 and CW_(min)=15, forthe Background or Best effort queues)

In a variant, factor CF may evolve within the range [1, CF_(max)] ifformula CWO=TBD* CWO_(min) is used, with CF_(max)=32 for instance.

Thus at steps 1407-1408, factor CF is updated upon each success/failureof OFDMA transmission.

In case of positive acknowledgment, the MU UL OFDMA transmission isconsidered as a success and step 1407 is executed during which factor CFis set to a (predetermined) low CF value, for instance 1 in case formulaCWO=TBD*CWO_(min) is used, or 0 in case formula CWO=2^(TBD)*CWO_(min) isused.

Otherwise, step 1408 (failing OFDMA transmission) is executed in whichfactor CF is doubled in case formula CWO=TBD*CWO_(min), or is increasedby one in case formula CWO=2^(TBD)*CWO_(min). In both cases, itcorresponds to the doubling of the corresponding CWO in case oftransmission failure. Note that factor CF is kept below CF_(max).

Note that further to step 1309 of handling properly the EDCA queuebackoff values, step 1310 is suppressed as the OBO computation is nowhandled in the initialization phase of steps 1401-1406.

This ends the process of FIG. 19.

The various alternative embodiments presented above with respect toFIGS. 14 to 20 are compatible one with each other, and thus may becombined to take advantage of their respective advantages. For instance,the triggering events (new trigger frame or new data in theAC/transmission buffer) and/or the updating of local CWO (directdoubling or through factor CF) of FIGS. 18 and 19 can be substituted onewith the other.

FIG. 21 illustrates, using a flowchart, third exemplary embodiments ofaccessing the medium based on the OFDMA medium access scheme and ofupdating the RU backoff parameters (e.g. CWO), either locally or basedon a received TBD parameter, when a new trigger frame is received. Thusit includes computing CWO by the node either through a local approach orthrough an AP-initiated approach (with the transmitted TBD parameter);it also includes switching between the two approaches.

In the third exemplary embodiments, a single transmission buffer isconsidered. It implies that steps 1304 and 1309 specific to themanagement of a plurality of AC queues are avoided.

Step 1700 is new compared to FIGS. 18 and 19. Steps 13xx and 14xx aresimilar to corresponding steps 13xx and 14xx described above.

Upon receiving a new trigger frame (step 1300), the node determineswhether or not OBO value is less or equal to 0 (test 1400), meaning thata new OBO value should be computed.

In case a current positive OBO value is running, meaning that the nodecurrently contends for access to the random RUs defined by the receivedtrigger frame, steps 1301 to 1308 are performed, similar to the processof FIG. 18 in case a single transmission buffer is used.

During this process, the local contention window size, namely local CWO,is updated depending on a success or failure in transmitting the data.

In particular, at step 1307, the local contention window size is set toCWO_(min) which preferably represents the number of random resourceunits defined in the received trigger frame. At step 1308, the localcontention window size CWO is doubled in case of transmission failure.For instance, when the local contention window size is determined as afunction of the number CWO_(min) of random resource units defined in areceived trigger frame, CWO=CWO_(min)* 2^(n) or CWO=CWO_(min)(t)*2^(n),where n is the number of successive transmission failures by the nodeand CWO_(min)(t) is the number of random resource units defined in thetrigger frame received at time t.

In case of zero or negative OBO value (test 1400), test 1401 determineswhether or not the received trigger frame includes a TBD parameter todrive the node in defining its own contention window size. This testmakes it possible to switch between a local approach and an AP-initiatedapproach to obtain CWO for computing a new OBO value (step 1406).

If the trigger frame does not include a TBD parameter (i.e. TBD field isset to UNDEFINED in the trigger frame), the current local value of CWO(as obtained through the last iteration of step 1307 or 1308) is used tocompute a new OBO value (step 1406) for contending for access to therandom RUs defined by the received trigger frame.

If the trigger frame sets a TBD value, step 1700 makes it possible tohandle the cases where the TBD value is restricted to a specific groupof nodes or a specific type of data or any other configurationparameter. Such information is included in the received trigger frame,for instance setting a BSSID as mentioned above for corresponding step1506 at the AP side.

In such a case for instance, the node checks whether a TBD parameterincluded in the received trigger frame is assigned to a group of nodesto which the node belongs. In particular, the checking step may includereading a BSSID, Basic Service Set Identification, in the receivedtrigger frame. This is step 1700.

Of course, other information can be read to determine whether or not theset TBD parameter should be applied by the node.

If the TBD parameter should not be applied, the new OBO value iscomputed (step 1406) using the local CWO value.

Otherwise (the TBD parameter should be applied), steps 1404 and 1405 areperformed to compute CWO_(min) and CWO, from the received TBD parameter.These steps are described above.

CWO_(min) may be equal to the number of random RUs in the receivedtrigger frame.

For instance, CWO=2^(TBD)*CWO_(min) or CWO=TBD*CWO_(min) or CWO=TBD orCWO is defined by the table entry having TBD as entry index, or CWO israndomly selected from [CWO_(min), CWO_(max)] where CWO_(min) orCWO_(max) equals TBD. Of course, the formula used may correspond to themere nature of the TBD value sent by the access point, in order for CWOto be preferably equal to CWO=2^(CRF)*CWO_(min), whereinCRF=α*(Nb_collided_RU/Nb_RU_total) as defined above.

Next to step 1405 or 1700 or 1401, the new OBO value can be computedbased on CWO newly obtained or on local CWO, when appropriate.

Next, the process loops back to step 1301 to actually contend for accessto the random RUs defined by the received trigger frame, given the newOBO value.

It is apparent from the above that in the embodiments of the invention,the management of the access to random RUs through RU backoff engines isfully distributed over the nodes. Furthermore it keeps compliancy with802.11 standard, in particular because the EDCA prioritization scheme iskept.

Note that the probability of collisions occurring over RUs, or even morelow usage of RUs, is monitored by the AP in some embodiments and fedback to the nodes through the TBD parameter. This makes it possible toconsider this overall network aspect for each individual medium accessat the nodes. This makes it possible to advantageously adapt the mediumaccess to improve OFDMA RU usage.

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

1-62. (canceled)
 63. A wireless communication method in a wirelessnetwork comprising an access point and a plurality of nodes, the methodcomprising the following steps, at one of said nodes: receiving atrigger frame from the access point, the trigger frame reserving atransmission opportunity on at least one communication channel of thewireless network, the trigger frame defining resource units forming thecommunication channel including a plurality of random resource unitsthat the nodes access using a contention scheme, wherein the node has abackoff value to be used to contend for access to the random resourceunits, in order to transmit data, based on a current backoff value,accessing a random resource unit to transmit data to the access point,after having transmitted the data, computing a new backoff value tocontend for new access to random resource units, the new backoff valuebeing a value randomly selected within a contention window range definedby a contention window size, wherein the contention window size isupdated depending on a success or failure in transmitting the data inthe random resource unit.
 64. The wireless communication method of claim63, wherein the contention window size is set to a low boundary value incase of transmission success.
 65. The wireless communication method ofclaim 64, wherein the low boundary value is predetermined.
 66. Thewireless communication method of claim 63, wherein the contention windowsize is doubled in case of transmission failure.
 67. The wirelesscommunication method of claim 66, wherein due to the doubling, thecontention window size equals CWO_(min)*2^(n), where n is the number ofsuccessive transmission failures.
 68. The wireless communication methodof claim 63, further comprising computing a new value for the contentionwindow size and a new backoff value upon receiving a new trigger framefollowing the step of transmitting data.
 69. The wireless communicationmethod of claim 63, wherein computing the new backoff value includesrandomly selecting a value within a contention window range [0, CWO],wherein CWO is the contention window size for the RU backoff value. 70.A communication method in a communication network, comprising an accesspoint and a plurality of nodes, at least one node comprising: aplurality of traffic queues for serving data traffic at differentpriorities; a plurality of queue backoff engines, each associated with arespective traffic queue for computing a respective queue backoff valueto be used to contend for access to the communication network in orderto transmit data stored in the respective traffic queue; and a secondbackoff engine different from the queue backoff engines, for computing asecond backoff value to be used to contend for access to at least onerandom resource unit splitting a transmission opportunity granted on acommunication channel, in order to transmit data stored in eithertraffic queue, the method comprising, at the node: computing the secondbackoff value by randomly selecting a value within a contention windowrange, wherein at least a size of the contention window range isdetermined based on at least one indication received from the accesspoint.
 71. The communication method of claim 70, wherein the size of thecontention window range is determined based on the indication receivedfrom the access point.
 72. The communication method of claim 70, furthercomprising receiving a trigger frame from the access point in thecommunication network, the trigger frame reserving the transmissionopportunity on the communication channel and defining resource units,RUs, forming the communication channel including the at least one randomresource unit.
 73. A communication device in a wireless networkcomprising an access point and a plurality of nodes, the communicationdevice being one of the nodes and comprising at least one microprocessorconfigured for carrying out the steps of: receiving a trigger frame fromthe access point, the trigger frame reserving a transmission opportunityon at least one communication channel of the wireless network, thetrigger frame defining resource units forming the communication channelincluding a plurality of random resource units that the nodes accessusing a contention scheme, wherein the node has a backoff value to beused to contend for access to the random resource units, in order totransmit data, based on a current backoff value, accessing a randomresource unit to transmit data to the access point, after havingtransmitted the data, computing a new backoff value to contend for newaccess to random resource units, the new backoff value being a valuerandomly selected within a contention window range defined by acontention window size, wherein the contention window size is updateddepending on a success or failure in transmitting the data in the randomresource unit.
 74. The communication device of claim 73, wherein themicroprocessor is configured to set the contention window size to a lowboundary value in case of transmission success.
 75. The communicationdevice of claim 74, wherein the low boundary value is predetermined. 76.The communication device of claim 73, wherein the microprocessor isconfigured to double the contention window size in case of transmissionfailure.
 77. The communication device of claim 73, wherein themicroprocessor is configured to compute a new value for the contentionwindow size and a new backoff value upon receiving a new trigger framefollowing the transmission of data to the access point.
 78. Thecommunication device of claim 73, wherein the microprocessor isconfigured, in order to compute the new backoff value, randomly select avalue within a contention window range [0, CWO], wherein CWO is thecontention window size for the new backoff value.
 79. A communicationdevice forming node in a communication network comprising an accesspoint and a plurality of nodes, comprising: a plurality of trafficqueues for serving data traffic at different priorities; a plurality ofqueue backoff engines, each associated with a respective traffic queuefor computing a respective queue backoff value to be used to contend foraccess to the communication network in order to transmit data stored inthe respective traffic queue; a second backoff engine different from thequeue backoff engines, for computing a second backoff value to be usedto contend for access to at least one random resource unit splitting atransmission opportunity granted on a communication channel, in order totransmit data stored in either traffic queue, computing the secondbackoff value including randomly selecting a value within a contentionwindow range, wherein at least a size of the contention window range isdetermined based on at least one indication received from the accesspoint.
 80. The communication device of claim 79, wherein the size of thecontention window range is determined based on the indication receivedfrom the access point.
 81. The communication device of claim 79, whereinthe microprocessor is configured receive a trigger frame from the accesspoint in the communication network, the trigger frame reserving thetransmission opportunity on the communication channel and definingresource units forming the communication channel including the at leastone random resource unit.
 82. A non-transitory computer-readable mediumstoring a program which, when executed by a microprocessor or computersystem in a device of a wireless network, causes the device to performthe method of claim 63.